Two police officers and one passerby were shot dead in the eastern Belgian city of Liege, according to the prosecutor's office.

The attacker opened fire outside a cafe before moving to a nearby college where he took a cleaner hostage, according to the public broadcaster RTBF.

The prosecutor's office said the man was "neutralised".

Two other police officers were injured.

The civilian who lost their life was the passenger of a vehicle that drove past the scene on Boulevard d'Avroy.

Authorities said terrorism could not be ruled out as a motive.

La Libre Belgique newspaper quoted a police source as saying the gunman shouted Allahu Akbar — God is greatest in Arabic — and RTBF said investigators believed the attacker may have had a terrorist motive.

Belgian Interior Minister Jan Jambon tweeted that authorities were "in the process of establishing exactly how things unfolded".