More than 400 people have died and 600 still missing after a mudslide swept away homes on the edge of the capital, Freetown, in one of Africa's worst flood disasters in living memory.

Crews continued the grim work of extracting bodies from tonnes of debris after fierce storms left impoverished, low-lying areas of Freetown buried.

Volunteers have been digging with pick axes and, at times, only their hands.

President Ernest Bai Koroma's office asked relatives to come to the city's morgue, saying that all unidentified corpses will be given a "dignified burial" in the coming days. He had called for seven days of mourning starting on Wednesday.

Sierra Leone's government has pleaded for international assistance as it reels from yet another disaster just a couple of years after the Ebola outbreak left thousands dead in the region.

The threat of further mudslides around Freetown remained. Many areas of the capital are near sea level and have poor drainage systems, which makes flooding worse during the rainy season.

Freetown also is plagued by unregulated construction of large residential houses in hilltop areas.

Deforestation for firewood and charcoal is another leading contributor to flooding and mudslides.