Five people are thought to have been killed when one of the Philippines' most active volcanoes erupted, throwing rocks on to a party of foreign climbers and their Filipino guides.

Several members of the party were also seriously hurt following Tuesday's eruption of the Mayon volcano in Albay province.

Three German climbers and a Filipino guide are among the dead, according to Albay provincial governor Joey Salceda.

Salceda said eight people had been injured and everyone was accounted for apart from one foreign climber who was missing, presumed dead.

A rescue operation is now under way to bring the climbing party down from the mountain.

"The injured are all foreigners. They cannot walk. If you can imagine, the boulders there are as big as cars," Salceda said, speaking from provincial capital Legazpi.

"We will rappel the rescue team, and we will rappel them up again."

The eruption was normal for the restive Mayon, said Renato Solidum, the head of the Philippine Institute of Volcanology and Seismology.

The 2,460-metre mountain, about 340km southeast of Manila, the capital, has erupted about 40 times during the past 400 years.

No alert was raised after the latest eruption and no evacuation was being planned, Solidum said.

Climbers are not allowed when an alert is up, and the recent calm may have encouraged this week's trek.

However, Solidum said that even with no alert raised, the immediate zone around the volcano is supposed to be a no-go area because of the risk of a sudden eruption.