Miyake Island's Mount Oyama erupted Thursday morning for the fourth time in just over a month, forcing nearby residents to evacuate, the Meteorological Agency said.

Smoke rising as high as 3,000 meters was seen moving eastward from the Izu island, and experts said it was the highest level of activity recently observed from the 813-meter volcano.

The smoke, initially gray but later turning black, was sighted by municipal officials at around 6:30 a.m., the same time the agency confirmed the eruption.

The meteorological observatory on Miyake Island said steam was followed by volcanic ash that fell on the northeastern part of the mountain.

Miyake Island authorities ordered about 630 people, or 315 households, to evacuate from the Tsubota and Kamitsuki areas shortly after 8:40 a.m.

The evacuation order was partially lifted in the afternoon.

At a morning news conference, Chief Cabinet Secretary Hidenao Nakagawa said the government will strengthen around-the-clock monitoring of volcanic activity and that the eruption is unlikely to become a catastrophe.

Meanwhile, the Yokohama regional headquarters of the Japan Coast Guard said it dispatched the patrol ship Yashima to the island. Helicopters from the Yashima will fly over the volcano to check for signs of damage, officials said.

Prime Minister Yoshiro Mori visited the government's crisis control center in the annex of the Prime Minister's Official Residence for a briefing on the situation.

"I'm worried that the attention of local residents may slacken as the protracted volcanic activity becomes a part of their daily lives," he said.

Miyake Island Airport has closed, and all four Air Nippon flights between Tokyo's Haneda airport and Miyake Island were canceled.

Earlier this week, the Coordinating Committee for the Prediction of Volcanic Eruptions warned of the possibility of small-scale volcanic eruptions. The volcano erupted three times in July.

Miyake Island and other islands in the Izu island chain have been hit by a series of quakes in past months.