Many people were killed Monday in twin suicide attacks targeting police in the capital of Chad, whose armed forces have been on the frontline of the fight against Boko Haram Islamists, police said.

The government swiftly convened an emergency meeting following the attacks outside the police headquarters and academy in N'Djamena, an official said on condition of anonymity.

There was no immediate claim of responsibility for the blasts, which a police official said left many dead and a number of people wounded.

It is believed to be the first attack of its kind in the capital of the north-central African nation, where security has been beefed up since Chad joined the fight against Boko Haram.

Members of Chad's security forces were seen taking up positions on the streets of the capital after the attacks, which came as President Idriss Deby was in South Africa for an African Union summit.

The former French colony is part of a four-nation coalition also including Nigeria, Cameroon and Niger that was created to tackle the Boko Haram insurgency.

Paris condemned Monday's blasts, with the foreign ministry saying in a statement it "stands alongside Chad and its partners in the fight against terrorism".

Last week, Abuja hosted a summit where Nigeria and fellow coalition members plus Benin rubber-stamped an 8,700-strong regional force to replace the current four-nation grouping.

The long-awaited Multi-National Joint Task Force, which was due to have been operational in November, has its headquarters in N'Djamena, under a senior Nigerian officer.

Boko Haram has been waging a six-year campaign of violence in northeastern Nigeria that has left at least 15,000 people dead and increasingly spilled across borders.

Chad's involvement in the coalition began earlier this year when Deby sent troops to assist neighbouring Cameroon, whose far northern region was coming under attack by the rebels.

Nigeria's new President Muhammadu Buhari, who has vowed to make crushing Boko Haram the priority of his rule, visited Chad earlier this month.

Buhari said "sustained and robust" regional cooperation was essential because of the cross-border threat posed by the Islamists.

Some of the 1.5 million people made homeless by the violence have fled to Chad, a poor, largely desert landlocked country.