President Teodoro Obiang Nguema said the explosion at 4pm on Sunday was due to the "negligent handling of dynamite" in the military barracks located in the neighbourhood of Mondong Nkuantoma in Bata.

"The impact of the explosion caused damage in almost all the houses and buildings in Bata," the president said in a statement.

The defence ministry released a statement saying a fire at a weapons depot in the barracks caused the explosion of high-calibre ammunition.

It said the provisional toll was 20 dead and 600 injured, adding that the cause of the explosions will be fully investigated.

The country's president said the fire may have been due to residents burning the fields surrounding the barracks.

State television showed a huge plume of smoke rising above the explosion site as crowds fled.

Images on local media seen by The Associated Press show people screaming and crying running through the streets amid debris and smoke. Roofs of houses were ripped off and wounded people were being carried into a hospital.

The Health Ministry made a call for blood donors and volunteer health workers to go to the Regional Hospital de Bata, one of three hospitals treating the wounded.

A doctor calling into TVGE, who went by his first name, Florentino, said the situation was a "moment of crisis" and that the hospitals were overcrowded.

Radio station, Radio Macuto, said on Twitter that people were being evacuated within four kilometres of the city because the fumes might be harmful.

Australian Associated Press