Indonesia's Mount Kelud volcano, which was put on the country's second-highest alert level last month, shows several alarming signs indicating it may erupt, the country's top volcano expert said.

"I'm scared about Kelud," said Surono, head of the Centre for Volcanology and Geological Hazard Mitigation in Bandung, in an interview with Reuters on Saturday.

"Kelud is now on the point of no return."

The number of volcanic earthquakes at Mount Kelud, 90 km (55 miles) southwest of Indonesia's second-largest city Surabaya, has risen to as high as 23 in one day, compared with a maximum of 15 a day just before its last eruption in 1990, Surono said.