At least 25 people are reported to have died in attacks by Nigerian militants Boko Haram.
The group made its first known lethal encroachment into neighbouring Chad in its latest wave of violence.
Dozens of jihadists arrived at a fishing village early in the morning on motorised canoes, setting houses on fire and attacking a police station.
A resident of Ngouboua village, around 12 miles east of Chad's border with Nigera, told Reuters: "They came on board three pirogues and succeeded in killing about ten people before being pushed back by the army."
Other local sources said the number of people killed was lower at between three and five.
Meanwhile, at least 21 people have reportedly been killed in two separate Boko Haram attacks in villages in northeastern Nigeria near the strategically important city of Maidiguri.
A community leader told AFP: "They killed 12 people in Akida village and nine others in Mbuta village during a raid".
He added that the group destroyed shops and homes in the raids.
The Sunni jihadist group has increased cross-border attacks in its attempt to create an Islamic caliphate around Lake Chad, which spans Nigeria, Chad, Cameroon and Niger.
The militants have proved a danger to any country bordering Nigeria.
Thousands of people were forced to flee the Niger border town of Diffa earlier this week following a wave of suicide attacks.
Chad's army, one of the best in the region, is involved in the battle against Boko Haram, as is Cameroon's elite rapid response unit Battalion D'Intervention Rapide.
Niger and Benin have also pledged military support, with a multinational force against the terror group set to be launched in the next few weeks.
