A strong explosion shook the Caspian Sea area where Azerbaijan has extensive offshore oil and gas fields late on Sunday.
A column of fire rose from the sea but Socar, Azerbaijan's state oil company, said none of its platforms were damaged.
The cause of the blast was not immediately clear, but Socar said preliminary information indicated it was a mud volcano.
The Caspian Sea has a high concentration of such volcanoes, which spew mud and flammable gas.
Socar spokesman Ibrahim Ahmadov was quoted by the Azerbaijani news agency APA as saying the blast took place about 10 kilometres from the Umid gas field, which is 75km off the coast of the capital, Baku.