A volcano erupted on a remote Japanese island on Friday, blasting black smoke thousands of metres into the sky and forcing residents to flee by boat and an airline to re-route flights.

A pyroclastic flow of super-heated gas and rock rolled down the side of Mount Shindake, on the southern island of Kuchinoerabujima, and into the ocean.

A 72-year-old man suffered minor burns to his face but there were no reports of other injuries among the island's 137 residents.

"It sounded like dynamite had exploded, and the house shook," one resident told TV Asahi.

Others described a smell of sulphur and clouds of smoke that blacked out the sky. Ash blanketed lower slopes and fell like snow on Yakushima, 12 kilometres to the east.

A video grab from the Japan Meteorological Agency's live camera image shows an eruption of Mount Shindake on Kuchinoerabujima island, Kagoshima Prefecture, on Friday. (Japan Meteorological Agency via Reuters)

Residents, many elderly and carrying boxes and bags, fled by boat to the closest neighbouring island of Yakushima, an hour away, where they disembarked shortly before sunset. Several struggled to control excited dogs on leads.

"All I could bring were a few emergency goods. It was utter chaos," one man told Fuji TV. "I'm really worried about things back home."

Smoke shot more than 9,000 metres into the sky and officials warned of more big eruptions and urged "extreme caution".

All Nippon Airways said it would divert some flights as a precaution but it did not cancel any. Japan Airlines said it did not have any plans to change flights.

Island the site of many eruptions in past

Kuchinoerabujima is about 130 kilometres south of Japan's southernmost main island of Kyushu, and 1,000 km southwest of Tokyo.

It was not clear if the eruption would affect the restart of Kyushu Electric Power's Sendai nuclear plant, which on Wednesday cleared the last of the nuclear regulator's safety hurdles, introduced after the Fukushima Daiichi nuclear plant disaster triggered by a March 11, 2011, earthquake and tsunami.

The company said the volcano posed no risk to the Sendai plant on Kyushu, and volcanologists agreed.

The island has seen several eruptions, including one in 1933 that killed eight people, but Mount Shindake was dormant for 34 years until last year.

Japan is one of the world's most seismically active countries and there has been an upsurge in volcanic activity in recent weeks, which volcanologists said may be linked to the big 2011 earthquake that set off a tsunami that killed nearly 20,000 people.

In 2014, 63 people were killed when Mount Ontake in central Japan erupted while packed with hikers.