Indonesian authorities raised the alert level on a volcano near the country's third largest city, the state volcanology office said Thursday.

"Since April 16, 2008, at 12:00 am (0500 GMT), we have upgraded the alert level of (Mount) Papandayan to 'vigilance' (level two)," a statement on the volcanology office's website said.

The alert level for the mountain, near the city of Bandung, is now two rungs below that for an impending eruption.

Papandayan rises 2,665 metres (8,743 feet) above sea level and is 51 kilometres (31.5 miles) southeast of Bandung city, which has a population of three million, while the greater Bandung area is home to about 4.5 million.

The mountain had not shown visual signs of activity but measuring equipment indicated an increased frequency of shallow volcanic quakes, the office said, adding that magma in the crater was also increasing steadily.

The office recommended an area within a radius of one kilometre from the crater be closed to the public.

A team was monitoring the volcano's activity, and no deaths had been reported, it said.

The Indonesian archipelago sits on the seismically active Pacific "Ring of Fire" where continental plates collide, and is home to about 130 active volcanoes.