A volcano on the remote southern Japanese island of Kuchinoerabujima erupted suddenly on Friday, blasting plumes of black smoke high into the sky, prompting authorities to start evacuating the island and airlines to re-route flights.

A pyroclastic flow of super-heated gas and rock flowed down the side of Mount Shindake and reached the ocean after the mountain's "explosive" eruption, but officials said there was no danger to human life.

One 72-year-old man suffered burns to his face after being caught in the pyroclastic flow, but there were no reports of other injuries among the island's 137 residents, whose only access to the outside world is by boat.

Watchful residents gathered on the roof of an evacuation center, its parking lot packed with cars, as the peak continued to spew out smoke and ash. Ash blanketed part of the mountain's lower slopes and fell on the main harbor, turning it grey.

Smoke billowed some 9,000 meters into the sky and officials warned of the risk of continuing, possibly large-scale eruptions, calling for "extreme caution".

Japan's All Nippon Airways said it would divert some flights to Okinawa and Southeast Asia as a precaution, but didn't plan to cancel any. Japan Airlines (JAL) said it did not have any plans to change any of its flights.

A ferry from Yakushima, the closest neighboring island about one hour sail east, had arrived and aimed to evacuate residents around 3:00 p.m. (0600 GMT), said Tatsuya Terada, a government official on Yakushima.

"We will need to verify safety conditions and check lists of names, but that's currently the plan," he said.

It was not immediately clear if the eruption would affect the restart of Kyushu Electric Power's Sendai nuclear plant, which on Wednesday cleared the last step of the nuclear regulator's stringent safety hurdles introduced after the Fukushima Daiichi disaster in 2011.

The company said an internal analysis showed the erupting volcano posed no risk to the Sendai plant on Kyushu island, and volcanologists agreed.

The island has been the site of several previous eruptions, including one in 1933 that killed several people.

Mount Shindake erupted last summer and the area where that pyroclastic flow occurred has been off limits since then.

Japan is one of the world's most seismically active nations and there has been an upsurge in volcanic activity in recent weeks, which volcanologists said may have been ushered in by the massive March 11, 2011 earthquake.

In September 2014, 63 people were killed when Mount Ontake in central Japan erupted without warning while packed with hikers.