Kiwi Michael Nutt arrived at work, directly beside Zaventem Airport in the Belgian capital, shortly after the deadly explosions on Tuesday night (NZ time).

The 25-year-old from Auckland moved to Brussels last August and works for an international logistics company.

"There was a constant stream of Police vehicles, military vehicles and ambulances that began wailing almost immediately and continued throughout the morning.

"People were rushing from the scene chaotically," he said.

"People were afraid there were more devices."

He said there was a lot of fear and confusion around but the area was quickly shut down.

"People immediately drew the connection between this attack and the arrest of the Paris terrorist leader."

Mr Nutt said people in Brussels have grown accustomed to the prospect of terror.

"Seeing armed, uniformed military personnel at bus stops is common- place here. There is a resilience which is amazing. But fear and anger is very visible.

"There have been murmurings of discontent over the capability of the police. But the handling of today's events has been seen as universally excellent."

New Zealand professional cyclists were also affected by the Belgium bombings and Rotorua's Sam Bewley says security fears remain for their upcoming races.

Bewley arrived two days ago at Brussels Airport and is staying about 70km away in Ghent preparing for races including the 100th edition of the Tour of Flanders on April 3.

He said cyclists would "try to carry on with what we do and stay strong - with respect to the victims.

"We've got a race scheduled for tomorrow and there are ongoing discussions with organisers at the moment," he said.

"If they decide to go ahead there will be some alterations - a moment of silence at the start, no podium celebrations at the end of the race."

Belgian authorities were last night hunting for a suspected Isis extremist whose bomb failed to explode in Tuesday's deadly terror attacks in Brussels.

Hundreds were injured and 34 people were killed in the attacks, which the Islamic State group yesterday claimed responsibility for.

Two suicide bombers, who police say were brothers Khalid and Brahim el-Bakraoui, exploded their devices at Zaventem airport about 8am Belgium time, and a third unidentified suicide bomber struck at Maelbeek metro station about an hour later.

The el-Bakraoui brothers from Brussels had a long history of organised crime in the Belgian Capital, local station RTBF reported, and were among the suspects being sought since last week's raids when Paris terror suspect Salah Abdeslam was arrested.

One of the el-Bakraoui brothers had rented a flat in Forest, southwest Brussels, which had been raided a week before Tuesday's attacks.

Abdeslam had been present at that raid and another cell member, Algerian Mohamed Belkaid, was shot by police.

One brother had also rented out the Belgian hideout in Charleroi used by the Paris attacks team.

RTBF reported one of the el-Bakraouis was also believed to have provided weapons and ammunition for the attack on an Eagles of Death Metal rock concert at the Bataclan.

Belgian Interior Minister Jan Jambon said last night the investigation into the airport attack was focused on three men who were seen pushing suitcase trolleys into the departure hall.

The two brothers, dressed in black with detonators thought to be concealed beneath their gloves, blew up their bombs in suicide attacks.

But the third man, who early reports have named Najim Laachraoui, was pictured in CCTV footage in a light-coloured coat and dark hat, fled after his bomb didn't explode. "We are now looking for this guy," Mr Jambon said.

Prosecutors said Laachraoui had been wanted by police since his DNA was found in properties used by the Paris attack cells last year.

He is reported to have travelled to Hungary with in September.

Zaventem mayor Francis Vermeiren said the suspects arrived at the airport in a taxi with bombs in their bags. "They put their suitcases on trolleys, the first two bombs exploded. The third also put his on a trolley but he must have panicked, it did not explode."

The taxi driver who dropped off the suspects at the airport reportedly led Belgian authorities to the extremists' address at Schaerbeek, in the north of Brussels. A raid of the property yesterday morning uncovered an explosive device with nails, an Isis flag and an unidentified chemical.

Belgian broadcaster VTM reported the suspects had ordered a large taxi, but were upset when it arrived because it was too small to fit all five of their pieces of luggage. The men had to leave one suitcase behind, which was found by police during the property search. The taxi driver was reported to have said the men would not let him touch their bags.

Medical officials treating the wounded said some victims lost limbs, while others suffered burns or deep gashes from shattered glass or suspected nails packed in with the explosives. Several children were seriously wounded.

Peter Mertens, of the Belgian crisis centre, yesterday said there was still a real and serious threat of more attacks. But people in the Belgian capital could start walking outside again and train stations would reopen.

Brussels airport remained closed yesterday, however, with damage to be assessed.

Isis said it had carried out "a series of bombings with explosive belts and devices".

The extremist group promised more attacks, saying: "What is coming is worse and more bitter."

The bombings came barely four months after suicide attackers, based in Brussels' largely Muslim Molenbeek district, slaughtered 130 people at Paris nightspots.

Intelligence agencies had warned for months a follow-up strike was inevitable. The arrest five days ago of Salah Abdeslam, a key suspect in the November attacks in Paris, heightened those fears, as investigators said many more people were involved than originally thought and some were still on the loose.

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