Police in Belgium are trying to determine what motivated a local man to open fire on a busy marketplace in Liege, killing at least four people.

Nearly 125 people were wounded, some critically, when 33-year-old Nordine Amrani fired bullets and hurled grenades.

Amrani died at the scene, but officials said he had not been shot by police. Some witnesses said he had shot himself in the head.

Police have said he was known to them for previous drugs and firearms offences and acted alone in the attack.

Amrani, a resident of Liege, had been jailed for 58 months in September 2008 for possessing firearms and drugs, media reports said.

Officials did not confirm this, but said they were aware he had spent some time in prison.

Prime Minister Elio Di Rupo said it had been "an isolated case".

The city is to hold a minute's silence and a vigil at midday on Wednesday.

A 15-year-old boy died instantly, while a 17-year-old boy and a 75-year-old woman died later in hospital.

An 17-month-old girl became the fourth victim late on Tuesday, dying in hospital despite undergoing hours of emergency treatment.

Belgium's Home Affairs Minister Joelle Milquet said four people remained in a critical condition.