Belgian authorities said they foiled a "terror attack" when soldiers shot dead a suspect after a small explosion at a busy Brussels train station that continued a week of attacks in capitals across Europe.

Key points: Suspect lay unattended after shooting for fears he had explosives

Suspect lay unattended after shooting for fears he had explosives The incident was being treated as a terrorist attack

The incident was being treated as a terrorist attack People standing near explosion were not injured

Federal prosecutor Eric Van der Sypt said soldiers "neutralised" a male suspect at the Central Station immediately after the explosion.

The man lay still for several hours while a bomb squad checked whether he was armed with more explosives.

The prosecutor's spokeswoman Ine Van Wymersch confirmed his death and said no other explosives were found on his body.

Belgian Army soldiers have helped lock down the area near Central Station. ( AP: Geert Vanden Wijngaert )

A public prosecutor, quoted by local media, said the man was wearing an explosive belt.

"An individual carrying a rucksack and an explosive belt in Central Station has been shot dead," the prosecutor said.

"He seems to have set off his device when the soldiers started paying attention to him."

Belgian federal prosecutors said the incident was being treated as a terrorist attack. The national alert level was maintained at its second-highest level.

A police spokesman said there was an explosion around a person before they were "neutralised by the soldiers that were on the scene".

Mr Van der Sypt said the man appeared to be 30 to 35 years of age but authorities had "no idea of his identity".

Local media reported that a bomb squad had performed a controlled explosion of an explosive belt the suspect had at the Central Station, and was checking to see if there were more hazards.

Station employee Nicolas Van Herrewegen told public broadcaster RTBF that he saw a man shouting in a lower level of the 1930s station, which serves lines running under the city centre.

He then appeared to yell "Allahu Akbar", Arabic for "God is great", and to detonate something on a luggage trolley.

People standing within three metres of the trolley were unhurt, Mr Herrewegen said.

Police investigators and members of the bomb squad work inside Central Station in Brussels. ( AP: Geert Vanden Wijngaert )

Belgian soldiers and police patrol outside Central Station. ( AP: Geert Vanden Wijngaert )

Reporters at the scene a little over an hour after the incident said the area was quiet, with police manning a cordon and a few bystanders calmly watching security forces at work.

Rail company spokeswoman Elisa Roux said that trains were being diverted from the station and replacement buses sent out to take passengers to the area.

The station and the adjacent historic downtown area Grand Place square, packed with tourists and locals on a hot summer evening, were evacuated as police set up a security cordon, witnesses told Belgian media.

Police evacuated people near the Grand Place near Central Station after the reported explosion. ( AP: Geert Vanden Wijngaert )

People speak with a police officer near Central Station. ( AP: Geert Vanden Wijngaert )

The city has been on high alert for more than 18 months since Brussels-based Islamic State militants carried out attacks in Belgium and France.

The March 22, 2016 bloodshed in Brussels hit Zaventem airport and a metro train killing at least 32 people, four months after bombings and shootings in Paris that killed 130 people.

Security experts said Tuesday's incident could have been similar to "lone wolf" assaults carried out by radicalised individuals with limited access to weapons and training.

"Such isolated acts will continue in Brussels, in Paris and elsewhere. It's inevitable," Brussels security consultant Claude Moniquet, a former French agent, told broadcaster RTL.

With Islamic State under pressure in Syria — where Belgium has been the most fertile European recruiting ground for foreign Islamist fighters — he said attacks in Europe could increase, though many of these would be by "amateurs" doing little harm.

He compared Tuesday's incident to that on Paris's Champs-Elysees avenue a day earlier, when a man was killed when he rammed his car, filled with explosive and weapons, into a French police convoy. No-one else was injured.

In London on Sunday (local time), a man was killed when a van was driven into a crowd of worshippers outside a London mosque, in what British Prime Minister Theresa May described as an "attack on Muslims".

Map Map showing Brussels Central Station and Grand Place square.

Belgian Army soldiers patrol outside Central Station. ( AP: Geert Vanden Wijngaert )

ABC/wires