Two explosions have torn through Brussels airport, killing at least 13 people, while a further blast struck a metro station in the capital shortly afterwards, killing 15 more.
Belgium's federal prosecutor confirmed in a press conference that the airport attack was carried out by a suicide bomber.
According to Belga news agency, shots were fired and Arabic-sounding words were shouted shortly before the two airport blasts at around 7am (8pm NZT) on Tuesday.
Social media showed pictures of smoke rising from the departure hall where all windows had been shattered by the blast. Passengers were seen running away down a slipway from the departure lounge, some still hauling their bags.
A third explosion took place at Maelbeek metro station, closing the entire metro system. The Belgian transport authority has confirmed 15 people were killed and 55 were injured in the blast.
All public transport in Brussels has been shut down, as it was in London during 2005 militant attacks on the underground that killed 52.
Clearly wary of another incident, the Belgian Crisis Centre has appealed to the population: "Stay where you are".
On the metro, traveller Evan Lamos tweeted a picture of passengers climbing from his train into the tunnel, saying: "We are being evacuated from the back of the metro, between Schuman and Maelbeek.
"Smoke in the tunnel as we evacuate."
The Maelbeek station is around 500 metres from the buildings of the European Parliament.
The blast went off on a carriage of the underground train, Belgian public broadcaster VRT reports. Other media reports cited the transport authority saying the explosion was on a train travelling between Schuman and Maelbeek stations, close to the EU institutions.
Metro operator STIB-MVIB has confirmed to media 15 people were killed in the blast and 55 more were injured.
Sixty New Zealanders are currently registered as being in Belgium, the Ministry of Foreign Affairs and Trade (MFAT) says.
There is no information yet on the nationalities of the victims.
Anyone concerned about friends or family in the region should attempt to directly contact them, MFAT says.
Airport authorities said the explosions caused several injuries, with witness reports saying the blasts occurred at a check-in desk.
Video shows the devastation inside the departure hall, with ceiling tiles and glass scattered across the floor. Some passengers emerged from the terminal with blood splattered over their clothes.
Airport spokeswoman Anke Fransen said: "There were two blasts in the departure hall. First aid team are in place for help."
Passengers were led on to the tarmac and the crisis centre urged people not to come to the airport.
Belgian media said rail traffic to the airport and flights out have been suspended.
Sky News television's Alex Rossi, at the scene, said he heard two "very, very loud explosions".
"I could feel the building move. There was also dust and smoke as well...I went towards where the explosion came from and there were people coming out looking very dazed and shocked."
"The thinking here is that it is some kind of terrorist attack -- that hasn't been verified by any of the authorities here at the airport."
Belgium has raised the terror threat alert level to level 4 -- the maximum. It's only the second time the terror threat level has been at level 4 since World War II; the first was following the Paris attacks.
The incident comes after the arrest of Paris terror attack suspect Salah Abdeslam in the city last week.
Belgium's Interior Minister Jan Jambon said on Monday the country was on high alert for a possible revenge attack following his capture.
"We know that stopping one cell can ... push others into action. We are aware of it in this case," he told public radio.
Belgian Prime Minister Charles Michel said on his Twitter feed: "We are following the situation minute by minute. Our priority concern is for the victims and those present in the airport."
European countries have responded to the attacks by moving to increase their own security measures.
France's Interior Minister Bernard Cazeneuve said his country would deploy 1600 security officers in response to the attack, while Denmark, Sweden and Finland have stepped up security at airports and in public places.
Newshub. / DPA / Reuters