More than 25,000 panicked residents have been evacuated from the slopes of a volcano on Indonesia's Sumatra island and officials have raised the alert level as the mountain's activity intensifies.

The heightened rumbling of Mount Talang coincided with a series of moderate earthquakes on Sumatra, which is still recovering from a massive 26 December quake and tsunami that killed nearly 130,000 people in Aceh province to the north.

Local officials said 26,000 people had been evacuated from the slopes and areas around the volcano in West Sumatra province, adding the number was likely to rise.

The volcano is near the city of Padang, 938km northwest of Jakarta.

Volcanologists said they could not confirm whether lava had spewed out. Smoke had billowed up to 1km above the volcano's crater, and ash had travelled up to 12km away, Surono said.

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

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, will visit the area later on Wednesday, officials in Jakarta 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 makeshift tents in open fields, while others took refuge at government buildings and sports stadiums in nearby towns. 

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

The mountain first began rumbling on Tuesday.

Indonesia, and especially Sumatra, has been hit by daily aftershocks since the massive earthquake on 26 December.

A quake off Sumatra on 28 March killed at least 676 people, many on Nias island off Sumatra's west coast.

Indonesia is a vast archipelago of about 17,000 islands that is along the geologically active Pacific Ring of Fire and has more than 100 active volcanoes.

PHOTO CAPTION

Merapi volcano in central Java, Indonesia. (AFP)