A tense Belgian capital was locked down for a second day Sunday with the police and troops patrolling deserted streets as authorities reviewed whether to extend a security alert meant to prevent a repeat of the bloody Paris attacks.

In Paris, defence minister Jean-Yves Le Drian said a chemical or biological attack “was among the risks” faced but that all possible precautions had been taken.

Belgian officials were to meet late afternoon to review the security alert, imposed over fears jihadists planned similar attacks to those in Paris which left 130 people dead on November 13.

The city’s metro system and public buildings were closed, along with shops and restaurants after the terror alert was raised to the highest level of four because of what officials said Saturday was an “imminent threat”.

The historic Grand Place in central Brussels, usually bustling, was virtually empty, with business badly hit in the run-up to Christmas as troops and armed police patrolled.

“A group of 140 called yesterday to cancel a booking. If it continues like this, the Christmas market will be called off with all the impact that could have,” said Patrick, a waiter at one of the many restaurants on the square.

Interior minister Jan Jambon said the authorities were looking not just for Paris suspect Salah Abdeslam who managed to slip past French security forces after the carnage in the City of Light.

“It involves several suspects and that is why we have put in place such exceptional measures,” the Belga news agency cited Mr Jambon as telling Flemish television. Justice minister Koen Geens said in a separate Belga report he expected the metro to re-open on Monday “if all passes off normally ... We are not going to paralyse Brussels economically.”

Two of the Paris suicide bombers, Brahim Abdeslam and Bilal Hadfi, had been living in Belgium. Fugitive suspected militant Salah Abdeslam, Brahim’s 26 year-old brother, slipped back home to Brussels from Paris shortly after the attacks.

Bernard Clerfayt, the mayor of the Brussels district of Schaerbeek, was quoted by broadcaster RTBF as saying there were “two terrorists” in the Brussels area ready to carry out violence.

Mohamed Abdeslam, the brother of Brahim and Salah, urged Salah in an interview on RTBF television to give himself up, adding that he believed Salah was still alive because he had had a last-minute change of heart while in Paris.

Belgium’s crisis centre, a state body that advises the government on security, said on Sunday the alert status for Brussels remained at its highest level of four, meaning a “serious and imminent” threat of an attack.