Saudi Arabia's navy evacuated dozens of diplomats from Yemen and the United Nations pulled out international staff on Saturday after a third night of Saudi-led air strikes trying to stem advances by Iranian-allied Houthi fighters.

Residents reported heavy clashes between the Houthis and mainly Sunni tribal fighters in the south of the country, while the Saudi-led air campaign sought to stall a fresh offensive by the Shi'ite Muslim group on Aden from the east.

Riyadh's intervention, a surprise move from a conservative monarchy better known for flexing its muscle in oil markets than through military might, is planned to last a month but could extend for five or six, a Gulf diplomatic source said.

Dozens of diplomats were shipped out of Aden to the Red Sea port of Jeddah, Saudi television said, escaping the city where President Abd-Rabbu Mansour Hadi had taken refuge until Thursday, when he left for Egypt to shore up Arab support for his crumbling authority.