Hundreds of Indonesians have begun evacuating the slopes of a rumbling volcano in East Java following increased levels of toxic fumes and tremors, a local rescue official said on Thursday (October 4). The country's volcanological survey raised Mount Kelud's alert status to the second-highest level on Sunday (September 30), following increased activity. "From right now the activity is increasing but not too significant. However we do see an increase in the normal condition level of the toxic fumes," said Surono, a surveyer in the volcano observation unit in Kediri. A mix of carbon dioxide and toxic substances seven times normal levels has been recorded from the volcano in recent days, prompting authorities to isolate the area. Local authorities in Kediri set up a briefing and field simulation to help people evacuate from the eruption of mount Kelud. "We prepared about 25 trucks for mobilisation," Talal Ali Santoso a local authority told journalists. The area was under tight security and people were refused entry. "We cleared the perimeter and made a data especially for local farmers here, we give zero tolerance for entering the zone", said Kediri Police chief Eky Fesianto. About 100,000 people, mostly farmers, live on the slopes of Mount Kelud which lies about 90 km (55 miles) southwest of Surabaya, Indonesia's second-largest city. Many people in the villages nearest to the crater, located on the borders of the safe zone, have already left their homes, local rescue official told Reuters. A 1919 eruption of Mount Kelud caused the lake in its crater to burst through the volcano rim and sent boiling water down its slopes, killing 5,000 people in 104 villages. Indonesia has the highest number of active volcanoes of any country, sitting on a belt of intense seismic activity known as the "Pacific Ring of Fire".