At least 187 people have died after an overloaded ferry sank off the Tanzanian island of Zanzibar with at least 800 people on board.

A government spokesman said 620 survivors had been rescued. Three days of mourning have been declared.

The MV Spice Islander was travelling between Zanzibar's main island, Unguja, and Pemba, the archipelago's other main island - popular tourist destinations.

It is thought to have capsized after losing engine power.