YOGYAKARTA (Agencies): Authorities warned that activity at Mount Merapi, Indonesia's most volatile volcano, was increasing on Sunday and told people living in its shadow to be ready for evacuation.

Mount Merapi, shared by densely-populated Central Java and Yogyakarta provinces, was spewing red hot rocks and huge clouds of ash as far four kilometers (2.5 miles) from the crater, said Suyono, a volcanologist at a monitoring post here.

The volcano is at its most active since it first showed signs of erupting almost two weeks ago, said Suyono, who like many Indonesians only uses one name.

Authorities have ordered people living around the 2,968 meters-high (9,737 feet) mountain to be prepared to leave at short notice.

Indonesian volcanology authorities on January 10 raised an alert on Mount Merapi to the second top danger level after increased volcanic activity.

The status was raised from "beware" to "be prepared."

The Indonesian vulcanology office recognizes four danger status for a volcano -- normal, beware, be prepared and alert -- the last being when signs of an immediate eruption appear.

The volcano has been declared off limits to mountain climbers but there has been no evacuation of the population living on the lower reaches of its slopes, Sunarto said.

Merapi last erupted in 1994 with heat clouds killing more than 60 people and forcing more than 6,000 people to evacuate to safer ground.

It also erupted in November 1976, killing 28 people and leaving 1,176 people homeless.