A volcano erupted on Wednesday on the same central Indonesian island struck last week by a powerful earthquake and tsunami, and authorities warned planes about volcanic ash in the air.

Mount Soputan on Sulawesi Island spewed a massive column of ash more than 6,000 metres (19,700 feet) into the sky.

No evacuations were immediately ordered.

A government volcanologist said it's possible the eruption was accelerated by the magnitude 7.5 earthquake that struck on Friday.

"It could be that this earthquake triggered the eruption, but we have seen an increase in volcanic activity since July and this began surging on Monday. Yet we can't say there a direct link, as the mountain is quite far away," Kasbani, the head of Indonesia's Volcanology and Geological Hazard Mitigation agency, said on local television.

Kasbani, who uses one name, said planes have been warned to avoid the area.

Nazli Ismail, a geophysicist at the University of Syiah Kuala in Banda Aceh on Sumatra island stressed there was no concrete evidence to show the two incidents are linked.

"People talk about the butterfly effect. The concept is that when a butterfly flaps its wings, it can cause a catastrophe," he said.

"So it is possible for the earthquake to trigger the volcano eruption, but it's not conclusive. This needs to be further investigated."

Danny Hillman Natawidjaja, a geologist with Indonesia's Institute of Science, echoed the views, saying there was not enough data to make a link.

"In principle, the seismic waves from the earthquake could increase pressure in the volcano's magma chamber and could cause an eruption. We don't know for sure," he said.

He cited the example of the eruption of Mount Talang volcano in Indonesia's Sumatra province in April 2005, which geologists have said was connected to the devastating December 2004 Indian Ocean earthquake and tsunami.

Ismail said the Soputan volcano eruption isn't surprising as Indonesia sits on the seismically active Pacific "Ring of Fire," and Soputan is one of the most active volcanoes on the island.

Soputan's eruption status was raised from an alert to standby 4 kilometres (2.5 miles) from the summit and up to 6.5km to the west-southwest.

Standby status means the public should avoid the area nearest the volcano and have masks available in the event of ash fall.

Planes were warned of the ash clouds because volcanic ash is hazardous for their engines.

Indonesia's national disaster agency spokesman, Sutopo Purwo Nugroho dismissed concerns that the volcano's eruption could affect planes transporting aid and supplies to the quake disaster areas.

The earthquake set off a tsunami and devastated several communities, with the official death toll rising on Wednesday to 1,407 and expected to increase further.

Thousands of others are injured and more than 70,000 have been displaced from their homes.

Nugroho said volcanic ash is not heading to the city of Palu, where most of the victims from the quake and tsunami are from, as the wind is blowing in another direction.

He said it hasn't disrupted plane services or affected any evacuations from the disaster areas.

Nugroho denounced videos that had appeared on social media allegedly showing villagers fleeing from billowing black smoke from the volcano and a long smoldering lava river as a hoax.

He said so far no lava has spewed out from Soputan.

No injuries or deaths have been reported and there is no need for any evacuation at the moment, he added.

Indonesia is an archipelago of more than 250 million people and government seismologists monitor more than 120 active volcanoes.