The blast was caused by a fire that erupted in a nearby truck terminal at around 10 p.m. local time then spread to the gas station and other buildings in Accra, National Fire Service representative, Prince Billy Anaglate, told JOYFM radio.
Many of the victims had sought shelter there from torrential rain, a fire brigade spokesman said.
Initial signs suggested the fire started by accident, he added.
Firefighters battled the blaze into the early hours while police and soldiers joined emergency crews helping rescue people trapped in the wreckage, said city Mayor Oko Vanderpuije.
Floods from several hours of heavy rains submerged buildings and vehicles across the city on Wednesday.
