Mount Oyama on Miyake Island in the Izu Island chain is likely to erupt soon, the Meteorological Agency warned Monday, forcing at least two-thirds of the island’s 3,850 residents to evacuate.

The island is about 200 km south of Tokyo.

The warning, which said the volcano could erupt within the next two hours, was issued at around 7:30 p.m. after a series of mild earthquakes shook the area. Such alerts are issued when volcanic activity becomes especially intense and urgent countermeasures are required.

“Based on past events, it is feared that a volcanic eruption could take place about two hours after successive earthquakes occur,” said Tsutomu Takeuchi, chief of the agency’s Volcanologic Division.

In response, the government set up a coordination office at the crisis management center in the annex of the Prime Minister’s Official Residence.

The Metropolitan Police Department responded by setting up a hazard patrol coordination office at 8:40 p.m.

The Japan Coast Guard, meanwhile, sent three patrol boats capable of carrying helicopters to waters around Miyake, and the Defense Agency has dispatched a rescue fleet of four destroyers.

The Tokyo Metropolitan Government said it asked islanders via a public announcement system at 8:45 p.m. to evacuate to nearby schools.

Miyake Island, with a population of about 3,850, is administered by the Tokyo Metropolitan Government. The island chain runs south of the Izu Peninsula.

The agency said the eruption would likely take place on the 814-meter volcano’s southwest slope.

The chief of the Miyake Municipal Government advised about 1,300 residents from the Ako district, in the southwest of the island, and about 1,100 resident from the Tsubota district, in the southeast, to evacuate to local school gymnasiums.

Police said all residents in the Ako district had evacuated by 10 p.m.

The local government also had buses and fishing boats standing by at Ako port in case of an eruption.

In the three-hour period beginning at 6 p.m., 269 temblors were detected on the island, 24 of which could be felt by humans, the agency said. The focus of the quakes is believed to have been in shallow waters off the island, it added.

The focus of the quakes is believed to have been in shallow waters off the island, it added.

Mount Oyama, the highest point on the island, last erupted on Oct. 3, 1983, destroying 413 of the approximately 500 structures in the Ako district of Miyake as lava gushed out of numerous craters. No one was injured.

Hidefumi Watanabe, a professor at the University of Tokyo, said Mount Oyama typically erupts soon after showing indications of seismic activity. In 1983, the eruptions commenced two hours after the first earthquake.

In the past, lava has flowed from vents in the middle of the mountain rather than from the top, which presents the danger that lava may flow to residential areas, Watanabe said.