Ninety-two Chadian soldiers have been killed in the deadliest attack ever by Boko Haram jihadists on armed forces in the country, President Idriss Deby Itno has said.

The attack is part of an expanding jihadist campaign in the vast, marshy Lake Chad area, where the borders of Cameroon, Chad, Niger and Nigeria converge.

Boko Haram launched an insurgency in Nigeria in 2009 before beginning incursions in its neighbouring countries to the east.

"We lost 92 of our soldiers, non-commissioned officers and officers," in the attack overnight Sunday in Boma, the president said on Tuesday. "It's the first time we have lost so many men," he added, after visiting the site of the attack in the Lac province, which borders Niger and Nigeria.

The attack on soldiers on the Boma peninsula lasted at least seven hours, and reinforcements sent to help out were also targeted. 24 army vehicles were destroyed, including armoured vehicles, and captured military arms were carried off in speedboats by Boko Haram.

"The enemy has hit at our defences hard in this zone," a senior officer said.

Boko Haram has stepped up its attacks in recent months on the islands of the Lake Chad basin. Boko Haram's insurgency has killed 36,000 people and displaced nearly two million in northeastern Nigeria since it began, according to the UN.

Since 2015, countries in the region have cooperated in the Multinational Joint Force, a regional coalition engaged around Lake Chad with the help of local residents formed into vigilante groups.