Gambia's Department of Water Resources reports torrential rain started on Saturday morning and continued for more than 20 hours in parts of the West African country.
The highest rainfall measured over that period was 276 mm (10.87 inches) at Banjul International Airport, compared with a previous record of 175.4 mm in July 1998, it said.
"It is the worst flooding I have ever seen in the Gambia," said Sanna Dahaba, executive director of the National Disaster Management Agency. "This is attributed to climate change, there's no doubt about that."
Two children died and an estimated 13,000 households were affected by the floods, he said, as heavy rain continued on and off throughout the country.
Gambia is highly vulnerable to the effects of climate change, including floods, drought, sea level rise and heatwaves, according to the World Bank. Its capital Banjul is situated on a peninsula where the Gambia River flows into the Atlantic Ocean.
Aerial photos and videos shared on social media showed vast areas of flooding with roads submerged and water nearly up to roof-level of some buildings.
The Gambia Red Cross said its volunteers were working around the clock to distribute supplies and help families relocate to emergency shelters.