"The status of Mount Talang is now at top alert," Surono, a vulcanologist from the Directorate of Vulcanology and Geophysics in the city of Bandung on Java island, told Reuters.

Officials also raised the alert level for Mount Tangkuban Perahu about 1,000 km (600 miles) away near Bandung because of increased activity but that volcano had yet to emit volcanic material.

Volcanic tremblings at the 2,076 metre (6,811 ft) Tangkuban Perahu had surged to 100 from two daily, Surono added. It was unclear if any residents would be evacuated.

Local officials said 26,000 people had been evacuated from the slopes and areas around the 2,690 metre (9,825 ft) Mount Talang in West Sumatra, adding that number was likely to rise.

Talang lies near the city of Padang, 938 km (528 miles) northwest of Jakarta, while Bandung is about 150 km southeast of Jakarta.

"It was like the end of the world," said Syafrudin, 65, a farmer, after fleeing from the mountainside and speaking outside a makeshift tent near the village of Tanjung Aua.

"I first heard the rumble and then the ground started shaking ... then there's smoke and sparks. We all ran in fear."

Vulcanologists said they could not confirm whether lava had spewed out. But smoke had billowed up to 1,000 metres (3,280 ft) from Talang's crater and ash had travelled up to 12 km (7.5 miles) away, Surono said.

"The activity has definitely stepped up and we have alerted airport officials to watch out for smoke," Surono said.

Scientists have warned of increased seismic activity in Indonesia as the plates that make up the earth's crust adjust following the magnitude 9 earthquake in December that triggered massive tsunami waves across the Indian Ocean.

"The plates' movements release energy underground and the energy could add to the activity of many volcanoes on Sumatra but it doesn't mean this will trigger an eruption," said Surono.

"Coincidentally, the pressure inside Mount Talang had been high and the quake activity has increased that energy."

FEAR AND PANIC

President Susilo Bambang Yudhoyono, who has urged Indonesians not to see the spate of quakes and the December tsunami as a sign of more natural calamities to come, visited some of the makeshift camps on Wednesday, witnesses said.

Elvi Sahlan, deputy mayor of the town of Solok near the volcano, said many residents were frightened.

"Up till 2 o'clock this morning we have evacuated around 26,000 people from the surrounding areas and the number is likely to increase because there are many others who have not been evacuated," Sahlan said.

Many residents spent the night in tents on open fields while others took refuge at government buildings in nearby towns.

"The whole family is stressed. It's better to be here now than to live in fear," said Yusmalidar, 40, who had just been evacuated in a government truck with his wife and three children.

One local official said there was a shortage of tents and water among residents.

The mountain first began rumbling on Tuesday.

Indonesia -- but especially Sumatra -- has been hit by daily aftershocks since the massive earthquake on Dec. 26. A quake off Sumatra on March 28 killed at least 676 people, many on Nias island off the island's west coast.