A mosque under refurbishment has collapsed in Somalia, killing at least 15 people and injuring 40.

It happened during Friday prayers as the building, in the capital Mogadishu, was packed with worshippers.

Hundreds of people are reported to have been inside the building when it collapsed and some are still believed to be trapped under the rubble.

An engineer on the refurbishment project has been arrested on suspicion of negligence, local media report.

Some media outlets report that worshippers were at prayer, while others say more than 100 people were pouring a concrete foundation after prayers when the structure collapsed.

Most of the dead were construction workers, the privately-owned Radio Shabelle reported.

The state-owned Somali National News Agency said the incident took place in Dayniile district.

Heavy rains have fallen on the area over the past few days.

The Somali government controls Mogadishu and other cities, but militants from the al-Qaeda-linked group al-Shabab dominate many rural areas.

More than 22,000 African Union soldiers and police are deployed in the country to protect the government.