A suicide attack on Yemen's defence ministry building has caused a large number of casualties, the latest reports say.

A suicide bomber drove up a car laden with explosives into the gate of the ministry building in the Bab al-Yaman district of the capital Saana, and triggered a heavy explosion, Reuters reported, citing eyewitnesses.

A ministry official said the explosion, which was followed by gun fighting, has caused "a large number of casualties", the report said.

Witnesses said ambulances have rushed to the scene of the explosion, the report said.

Yemen has been facing strident al-Qaida-backed insurgency ever since the government forces pushed back militants from some of their southern strongholds with US help.

Earlier this week, six suspected al-Qaida militants and three Yemeni soldiers were killed in clashes in the country's eastern region of Hadramout, Reuters had reported.

The al-Qaida in the Arabian Peninsula (AQAP) has strongholds in southern Yemen, but the impoverished Arabian Peninsula state is also challenged by the Houthi rebellion in the northern region.