A makeshift displacement site in the 9th district of N Djamena. Photo: IOM
"Recent rainfall has affected more than 341,000 people in 11 of the 23 provinces of Chad," the UN's humanitarian agency OCHA said in a statement.
This meant they had to "abandon their homes" or "lost possessions", the OCHA office in Chad told AFP.
Last week, OCHA said torrential rains had killed 22 people in Chad since June.
The capital N'Djamena, which is located near the Chari river, has been the most badly affected by the downpours.
Several neighbourhoods were flooded earlier this month after torrential rain hammered the city for more than a week.
Last year, 256,000 people suffered damage during floods, while up to 388,000 people were affected in 2020, the agency said.
Some 5.5 million Chadians, around a third of the landlocked central African country's population, needed "urgent humanitarian assistance" last year, according to the United Nations.
The situation has worsened because of the war in Ukraine, with challenges bringing Ukrainian grain to foreign markets.
Chad, which has seen numerous armed conflicts since independence from France in 1960, is the third least developed country in the world, the UN says.