Belgium's PM: This is a dark moment

A metro train damaged by an explosion on the Brussels Metro 22 March 2016. Photo: alxdm/Twitter

Belgium's Prime Minister said his country had been plunged into a "dark moment" after suicide blasts rocked the capital tonight.

Charles Michel told a televised press conference that "scores" of people had been killed in the attacks at Brussels Airport and a metro train station.

"What we feared has happened - we were hit by blind attacks," he said.

"We know there are many dead, many injured," he said.

"This is a dark moment for our nation. We need calm and solidarity."

Mr Michel said military reinforcements had been deployed and border controls reinforced.

He had warned on Monday that the struggle against Islamic militants in his country didn't stop with the capture of suspected Paris attacker Salah Abdeslam.

There were hundreds more radicalised people in Belgium on a list compiled by risk analysis agency OCAM, which had maintained its "high" threat level even after special forces ended their four-month manhunt for Abdeslam.

"We are faced with a new page of the history of Europe with real threats," Mr Michel told RTL TV.

"There is a huge work for the secret intelligence services to foil terror attacks."

Abdeslam, believed to be the sole surviving participant of the November massacre that left 130 people dead, was dubbed Europe's most wanted man after going to ground in the days after the Paris assault.

He sustained a wounded leg as special forces hauled him out of a bolthole in his home neighbourhood - the immigrant-heavy Brussels suburb of Molenbeek, seen as a hot spot for Jihadists and routinely neglected by past governments.

French Interior Minister Bernard Cazeneuve said at the weekend that the terror threat remained "extremely high" despite a series of arrests since the Paris attacks and "intense" operations by police to dismantle networks used for recruitment.

Belgian prosecutor Frederic Van Leeuw echoed the warnings, saying on RTL TV that the end of the hunt for Abdeslam shouldn't be greeted by "triumphalism".

Belgian Foreign Minister Didier Reynders said at a conference on Monday that information gleaned following Abdeslam's capture indicated "that he was ready to restart something from Brussels".

This "may be the reality," he said, because "we have found a lot of heavy weapons in the first investigations and we have seen a new network of people around him in Brussels".

Mr Michel, facing criticism over his nation's failure to catch Abdeslam sooner and inability to foil homegrown radicals, vowed to focus energy on countering terrorism in the Belgian capital.