BRUSSELS (AFP) - Belgian ministers under fire for intelligence failings over the deadly Islamic State suicide attacks on Brussels admitted "errors" and offered to resign on Thursday as police hunted two suspects still at large after the bombings.

With criticism growing that international security authorities failed to follow links between Tuesday's bombings and similar attacks that hit France in November, key Paris suspect Salah Abdeslam insisted he was unaware of plans to strike the Belgian capital.

Grieving Belgians observed a minute of silence on the third and final day of mourning for the 31 people killed in the attacks on the airport and a metro station in the symbolic heart of Europe, putting security agencies across the continent on edge.

Several hundred people gathered at the central Place de la Bourse square, strewn with candles, balloons and flowers as flags from several nations fluttered from the columns of the stock exchange building.

"Our love for Brussels is stronger than terror," read one banner held by a grieving young couple.

As pressure mounted on Belgium's government over claims it ignored the deportation of airport bomber Ibrahim El Bakraoui from Turkey in 2015 as a "foreign terrorist fighter", the interior and justice ministers tendered their resignations.

"There were errors at Justice and with the (Belgian) liaison officer in Turkey," Interior Minister Jan Jambon was quoted as telling the Le Soir daily on Thursday, confirming that he and Justice Minister Koen Geens had both offered to quit.

Prime Minister Charles Michel, who turned down their offers, pledged the government would "shed light" on the handling of the attacks, given that three of the perpetrators were already known to police.

The Belgian blunders have implications for the rest of Europe, with evidence deepening by the day that both the Brussels and Paris cells were the work of a huge jihadist cell based out of Brussels.

Police arrested Abdeslam just around the corner from his family home in Brussels on Friday, after he spent four months on the run following the attacks on Paris which killed 130 people.

Abdeslam's lawyer Sven Mary said Thursday his client, the last known survivor of the 10 men who carried out the bloody assault on the French capital, now did not want to fight extradition to Paris.

Asked if Abdeslam had prior knowledge of Tuesday's assault on Brussels, Mary replied: "He didn't know it".

However Abdeslam is said to have links to Ibrahim El Bakraoui and his brother Khalid, who bombed Maalbeek metro station.

Despite earlier saying the El Bakraoui brothers were only known for criminal activity, prosecutors admitted on Thursday that they had issued an international warrant for Khalid in December for terrorism in relation to the Paris attacks.

They also confirmed Khalid rented out a flat used by the Paris cell in the Belgian city of Charleroi, while he is further reported to have hired a Brussels apartment raided in the hunt for Abdeslam last week.

Belgian authorities are now hunting a man with a large bag seen talking to Khalid El Bakraoui on CCTV footage at Maalbeek station, who then did not get on to the train, police sources told AFP.

A huge manhunt is already under way for a third attacker at Brussels airport, a man wearing a hat seen on security footage with Ibrahim El Bakraoui and a man identified as Paris bomb-maker Najim Laachraoui, but whose bomb did not go off.

The attacks have stunned Brussels, the symbolic heart of Europe and home to the headquarters of the EU and Nato.

The city remained on maximum alert with soldiers in camouflage standing guard outside embassies and government offices and underground rail services cut between 7pm and 7am, forcing commuters to scramble for the last trains home.

Outside the bombed metro station of Maalbeek, just a few hundred metres from key EU institutions, a banner read "why?" in English, French and German.

EU justice and interior ministers convened later Thursday in Brussels for an emergency meeting to show "solidarity" to Belgium and work out a plan to address the threat to Europe posed by jihadists.

The terrorism threat adds to the mountain of problems facing the continent, already grappling with its worst ever migration crisis.

Belgian Foreign Minister Didier Reynders said the attacks, the worst in the country's history, had killed or wounded people of around 40 nationalities, with doctors saying they were treating injuries "seen in war." Very few of the dead have been formally identified but stories were emerging of lucky escapes and tragic ill fortune of people caught in the wrong place at the wrong time.

A young German couple headed for a New York holiday were among the victims of the Brussels airport attack, which left the wife missing and the man in a coma, the Bild daily reported.

It identified the couple by their first names as Jennifer, 29, a sales employee, and Lars, a 30-year-old hospital nurse, and said they had looked forward to the US trip after they married last year.

Adelma Marina Tapia Ruiz, a 37-year-old Peruvian woman, was killed by the airport bomb but her two young daughters and husband survived because the twin girls had run off and the father was chasing after them.

Doctor Muriel Brugmans, who tried to save her life in hospital, said on Facebook: "Tonight I'm thinking very much about my patient, mother of two adorable little girls. She was... so worried for her daughters."

The health ministry said on Wednesday that the number of people injured had climbed from 270 to 300, 61 of whom were in critical condition.