An explosion killed at least six people at Somalia's newly reopened national theatre in Mogadishu on Wednesday during an event attended by government officials, the African Union force in Somalia said.

A Reuters reporter at the scene said corpses were strewn across the floor and some of the dead were still in their chairs. Ambulance workers were collecting the bodies.

So far six died and 10 were injured, mostly civilians. The Prime Minister was speaking inside the theatre when the blast took place, but he is safe, unhurt, Prosper Hakizimana, deputy spokesman for the AU's AMISOM force, told Reuters.

Ambulance sirens wailed as the wounded were rushed to hospitals.

A doctor at the Madina hospital said two ministers and a member of parliament were among those hurt. Initial witness reports suggested a suicide bomber was behind the blast.

One witness at the theatre, Said Mugambe, told Reuters he could see four corpses.

Somalia's National Theatre reopened on March 19 for the first time in 20 years, an event the government said signalled a marked improvement in security in the war-ravaged Horn of Africa country.

But al Shabaab rebels, who pulled out of the capital last August, have continued to strike targets in the heart of the coastal city using roadside bombs, mortars and suicide bombers.

Al Shabaab said on March 14, after one its suicide bombers struck at the presidential palace, that more explosions and bombers would follow.

The presidential palace has come under mortar attack several times in the last two weeks. The bombs have mostly fallen short, killing civilians in nearby camps for those displaced by the violence.

(Additional reporting by Abdi Sheikh in Mogadishu and Mohamed Ahmed in Nairobi; Editing by David Clarke and Alistair Lyon)