Saudi civil defence authorities have been evacuating villagers from a volcanic region in the west of the kingdom after a series of strong tremors this week sparked fears of a major quake, local media said on Wednesday.

The Saudi authorities have reported no casualties from the seismic activity so far but a total of 46 tremors were recorded on Tuesday, the Saudi Geological Survey said.

The US Geological Survey said it had recorded a quake measuring 5.7 on the Richter scale at 1735 GMT on Tuesday, with its epicentre 216 kilometres (135 miles) west-northwest of the Muslim pilgrimage city of Medina.

Saudi media had reported a previous strong tremor in the region on Sunday.

The civil defence authorities ordered the evacuation of residents of settlements within a 40 kilometre (25 mile) radius of the epicentre and have set up camps to house them until they can be moved to more permanent shelters in the region's larger towns.

Some 800 people have already been evacuated from the Al-Qarasa, Al-Hadama and Al-Amid districts and put in hotels or apartment blocks in the Red Sea city of Yanbu, the area's civil defence director Essam Farrash told the Arab News daily.

State television aired footage of the camps showing local officials attempting to reassure evacuated residents.

The area has a number of dormant volcanoes and the Saudi Geological Survey said that the past week's tremors had been accompanied by increased volcanic activity with rising heat levels and gas emissions.