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May 29, 2015, 2:49 AM UTC / Updated May 29, 2015, 11:47 AM UTC

Japanese authorities ordered all of the people on a small island to evacuate after a volcano erupted Friday morning in a towering plume of thick, black smoke almost six miles high and a shower of fiercely hot rock and toxic gases.

Japan's main government spokesman, Chief Cabinet Secretary Yoshihide Suga, told reporters that all 137 people believed to be on the southern island of Kuchinoerabu were confirmed safe. Prime Minister Shinzo Abe set up a task force to coordinate operations.

The national broadcaster NHK broadcast a bulletin showing smoke billowing over Mount Shindake, which the Japanese Meteorological Agency said erupted violently at 9:59 a.m. (8:59 p.m. ET).

At a news conference late Friday morning, Sadayuki Kitagawa, director of the Meteorological Agency's volcanology division, characterized the eruption as one of "explosive power," with a smoke plume rising 9,000 meters, or almost 30,000 feet, from the crater.

Kitagawa said a pyroclastic flow — a fluidized mixture of blazing rock fragments and toxic gases — was flowing from the volcano and had reached the island's northwest coast.

He said the alert level of 5, the highest on the scale, was being maintained because more powerful eruptions are possible.

Kuchinoerabu is part of the remote Ryukyu archipelago south of the mainland. Access to the island is only possible by boat, and a nearby ferry service is expected to be diverted to begin evacuating the island's residents.