Mayon Volcano in the central Philippines' Bicol region spewed ash on Tuesday morning (May 7), killing four German hikers and their Filipino guide, the national disaster agency said, adding that seven others were injured.

The agency said the ash explosion lasted about 73 seconds, as gray and brownish clouds rose up to 500 meters (0.31 miles) above the summit.

The steam-driven explosion is not serious and is caused by trapped water and rainfall that entered the crater, the chief of the Philippine Institute of Volcanology and Seismology said (PHIVOLCS).

There were casualties among 27 hikers who climbed Mayon Volcano and called to be rescued. Disaster officials had sent a helicopter to the site..

Mayon Volcano is a popular tourist destination and hikers often camp on the slopes before heading to the summit.

There is a permanent danger zone of 6-km (0.62-miles) around the volcano, and PHIVOLCS discourages hikers from climbing it.

Mayon's last major eruption was in December 2009, when it ejected lava and high levels of sulfur dioxide as hundreds of volcanic quakes were recorded for a sustained period

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