MIAMI, Florida (CNN) -- Hurricane Rita's winds were at 175 mph Thursday as it spun closer to the Texas coast -- where it is projected to make landfall early Saturday -- and as thousands of residents began streaming from the Gulf Coast.

At 5 a.m. ET Thursday, the maximum sustained winds for the Category 5 storm were 175 mph -- equivalent to the maximum strength of deadly Hurricane Katrina at its peak, according to CNN meteorologist Jacqui Jeras. Rita's gusts were even higher.

"Rita is a potentially catastrophic Category five hurricane on the Saffir-Simpson scale," the National Hurricane Center (NHC) said in its latest advisory. A storm becomes a Category 5 when its wind speeds reach 155 mph.

If the storm maintains its intensity, Rita "could be worse than Katrina," which devastated southeast Louisiana and coastal Mississippi a little over three weeks ago, said Max Mayfield, director of the hurricane center.

More than 1,000 deaths are blamed on Katrina, which struck August 29.

Mayfield said the long reach of Hurricane Rita's winds may begin making evacuation difficult by Friday, so residents who need to evacuate should plan to leave Thursday.

Forecasters expect the center of Rita to make landfall somewhere between the Texas cities of Corpus Christi and Galveston. But because of the power and size of the hurricane -- which has a tropical wind field 370 miles wide -- the effects will likely be felt far from the point of landfall. (Watch how Galveston is in a precarious location -- 1:58)

Galveston, a city of 60,000 people, was flattened by an infamous hurricane in 1900. (Watch a report on the storm of the century -- 2:00)

On Wednesday night, forecasters said Rita had become the third most powerful hurricane recorded in the Atlantic Basin, based on its central pressure.

Wind speeds accelerate as a hurricane's internal pressure -- measured in millibars -- decreases, pulling high pressure air into the low-pressure center of the storm.

According to the hurricane center, Rita -- with 898 millibars of pressure -- ranks only behind Hurricane Gilbert in 1988 with 888 millibars and the 1935 Labor Day hurricane with 892 mb.

At 5 a.m. ET Thursday, Rita's eye was 515 miles east-southeast of Galveston and about 615 miles east-southeast of Corpus Christi, moving west-northwest at 9 mph, according to the hurricane center. The storm was expected to shift more to the northwest late Thursday and into Friday.

Although Rita is expected to make landfall early Saturday between Galveston and Corpus Christi, the National Hurricane Center has not ruled out an impact for Louisiana, where post-Katrina recovery efforts are continuing.

A hurricane watch for Rita was in effect for nearly the entire coast of Texas from Port Mansfield, north of Brownsville, to Cameron, Louisiana, just east of the state line. The watch means hurricane conditions, including sustained winds of at least 74 mph, are possible within 36 hours.

A tropical storm watch was in effect on either side of the hurricane watch area.

Hurricane-force winds were extending outward for up to 70 miles from the center, and tropical storm-force winds were extending up to 185 miles.

Although tides were near normal along the Mississippi and Louisiana coasts in the areas affected by Katrina, tides were to increase 3 to 4 feet and be accompanied by large waves during the next 24 hours, and residents could experience coastal flooding, the hurricane center said.

Heavy rains were to begin swamping the western and central Gulf coastal areas Thursday night into Friday. Forecasters expected Rita to produce rainfall accumulations of 8 to 12 inches -- with isolated maximum amounts of 15 inches -- over the central to upper Texas coast. Rainfall amounts of 2 to 24 inches were possible across southern Louisiana, including the New Orleans metropolitan area.

After Rita moves inland, the hurricane center said, rainfall amounts of 5 to 10 inches are possible over eastern Texas and central and eastern Oklahoma Saturday and Sunday.

'We've got to be ready for the worst'
The White House declared a state of emergency for both Texas and Louisiana late Wednesday, authorizing the Federal Emergency Management Agency to send resources into both states.

"We hope and pray that Hurricane Rita will not be a devastating storm, but we've got to be ready for the worst," Bush said during a speech to the Republican Jewish Coalition in Washington. (Watch video on President Bush's response to Rita -- 2:26)

Rita dealt a glancing blow to the Florida Keys on Tuesday. At least 100 homes in Key West were flooded by about 3 feet of water, but there was otherwise no major damage, Mayor Jimmy Weekley said. Once past the Keys, the hurricane rapidly gained strength Wednesday as it churned over the Gulf's warm waters, becoming the fifth major hurricane of the busy 2005 season.

Category 5 storms -- which can generate storm surges higher than 18 feet and can cause catastrophic damage to buildings -- are rare. Only three such monsters have made landfall in the United States in the past 70 years, including Andrew in 1992, Camille in 1969 and the unnamed storm that hit the Florida Keys in 1935.

Texas Gov. Rick Perry urged residents in his state's coastal communities to begin making urgent evacuation plans.

Thousands of people, including some who fled Hurricane Katrina last month, streamed out of Galveston and other Texas towns Wednesday. (Watch Galveston residents prepare for Rita -- 1:22)

"I'm prepared to be gone two weeks or more, and I have medication and everything my kids need to prepare myself for that," said Julia Marshall, who moved to Galveston earlier this year from New Orleans with her five children.

City officials say about 3,000 Louisiana residents evacuated to Galveston before or after Hurricane Katrina struck August 29. They have been uprooted a second time. (Watch a two-time evacuee discuss her situation -- 6:49)

More than 10 patients at a Texas nursing home were being taken to a Houston hospital after they fell unconscious when carbon monoxide came through the vents of the bus evacuating them, a police dispatcher said.

Police in La Porte, Texas, were notified of the incident about 9:20 p.m., said dispatcher Shawntel Robertson. The first call reported a patient having a seizure, she said, and others reported unconscious patients.

About 15 people were "unconscious and unresponsive" when police arrived, she said.

The patients were being taken to Hermann Hospital in downtown Houston, about 22 miles west of La Porte, with a police escort, she said.

FEMA teams head to Texas
Corpus Christi Mayor Henry Garrett signed mandatory evacuation orders Wednesday for 250,000 people in that Texas coastal city and the rest of Nueces County. Garrett said the 13,000 to 15,000 residents of Padre and Mustang islands and low-lying areas of Corpus Christi must leave their homes by 2 p.m. (3 p.m. ET) Thursday. The rest have until Thursday evening to leave.

Garrett said he is ordering the evacuations at least a day earlier than he normally would because of the disaster wrought by Katrina, which is blamed for more than 1,000 deaths.

Meanwhile, Homeland Security Secretary Michael Chertoff said he has designated Rear Adm. Larry Hereth, the Coast Guard's director of port security, as the primary federal official for Rita response efforts.

"It's really all hands on deck to deal with this storm," Chertoff said. "We've now prepositioned or are in the process of prepositioning a lot of supplies. We've got helicopters on standby." (Watch Chertoff explain what's been learned since Katrina -- 3:50)

R. David Paulison, acting undersecretary for homeland security, said support teams and supplies were being relocated from Florida to Texas as Rita's landfall nears.

Fourteen urban search-and-rescue teams, with a total of 800 members, and 400 medical personnel were being put in place, he said.

He said the Department of Defense was helping to set up field hospitals to accommodate 2,500 beds, providing materials to build temporary bridges in case of serious damage to infrastructure, and organizing food kitchens. In addition, the Department of Transportation was providing buses for evacuations.

Paulison said 45 truckloads of water, 45 truckloads of ice and 25 truckloads of ready-to-eat meals were being staged in Texas. Communications teams were in place in case of electrical outages.

"I strongly urge Gulf Coast residents to pay attention to this storm," Paulison warned. "Listen to your state and local officials. If they ask you to evacuate, please do so immediately."

Paulison urged residents to prepare for the storm by consulting the www.FEMA.gov or www.ready.gov Web sites, which list items families should have.

"We need to be sure you have a communications plan for your family," he said. "Know how you're going to contact each other" after the storm hits.

Ernie Allen, president of the National Center for Missing and Exploited Children, said one of the lessons learned from Katrina was that families need to take some pictures with them.

He also advised parents to make "a little simple ID for your child" that they can keep with them in case they become separated. (Full story)