Flash flooding in Somalia has killed 50 people and driven nearly 700,000 from their homes, a government official said, with heavy rains starting Tuesday expected to worsen the country's plight.

The Horn of Africa region is experiencing torrential rainfall and floods linked to the El Nino weather phenomenon, claiming dozens of lives and causing large-scale displacement, including in Somalia, where the downpours have destroyed bridges and inundated residential areas.

"Fifty people died in the disaster... while 687,235 people were forced to flee their houses," Somali Disaster Management Agency director Mohamud Moalim Abdullahi said at a press briefing on Monday.

"The expected rains between 21st and 24th of November... may cause more flooding which could cause death and destruction," he added.

On Saturday, the UN humanitarian agency OCHA said the number of people displaced by heavy rains and floods in Somalia "has nearly doubled in one week", while 1.7 million people overall have been affected by the disaster.

"In addition, roads, bridges and airstrips have been damaged in several areas, affecting the movement of people and supplies and leading to increased prices of basic commodities," OCHA said.

British charity Save the Children on Thursday said more than 100 people, including 16 children, had died and more than 700,000 forced from their homes in Kenya, Somalia and Ethiopia due to flash flooding.

The Horn of Africa is one of the regions most vulnerable to climate change and extreme weather events are occurring with increased frequency and intensity.

The region is emerging from the worst drought in four decades after multiple failed rainy seasons that left millions of people in need and devastated crops and livestock.

Humanitarian groups have warned that the situation is only likely to worsen and called for urgent global intervention as El Nino is expected to last until at least April 2024.