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(CNN) -- Five people have been killed after one of the Philippines' most active volcanoes spewed a giant cloud of ash and rocks early Tuesday.

They were climbing on Mount Mayon, some 212 miles (340 km) southeast of Manila, when the blast occurred at around 8 a.m. local time, according to the National Disaster Risk Reduction and Management Council (NDRRMC).

Of the five fatalities, four were German tourists, while the other was identified as Jerome Berin, their Filipino guide, the NDRRMC said. Joey Salceda, governor of Albay Province, told CNN affiliate ABS-CBN they were killed after being hit by falling rocks. He said they were part of a larger group scaling the volcano. Seven others, including an Australian, were hurt.

The NDRRMC said a total of 27 hikers were on the volcano at the time and requested assistance.

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According to the Philippine Institute of Volcanology and Seismology, the blast sent a thick column of ash 500 meters (1,600 feet) into the air -- the result of what it called a "small phreatic event" that lasted about 73 seconds.

While no intensification of volcanic activity was observed, it warned that these sudden ash and steam explosions could occur at any time. Therefore officials advised people against going inside a six-kilometer danger zone around the volcano.

Mount Mayon is the most volatile of more than 50 volcanoes -- 22 of which are considered active -- that are scattered across the Philippine archipelago.

An almost perfect cone shape, Mayon last erupted in 2010 and forced thousands of people to flee from their homes. Mayon's slopes, like many volcanoes in the country, are home to thousands of farming communities who make use of the fertile soils provided by the volcanic activity despite the occasional risk of eruption.