An eruption of a volcano on Miyake Island in the Izu Island chain off Tokyo is expected within two hours, the Meteorological Agency issued an emergency alert Monday evening. The Japan Coast Guard dispatched cruisers and helicopters to rescue islanders in the event of an eruption.

The agency said a constant series of temblors has been monitored on the island, indicating that the quakes are related to volcanic activity and that its volcano may erupt for the first time in 17 years.

The agency issued the volcanic alert at around 7:30 p.m. Such alerts are issued when volcanic activities become extremely high and urgent countermeasures to prevent or mitigate damage to human lives are required.

Mount Oyama on the island erupted on Oct. 3, 1983, gushing out a flood of molten lava from the volcano and sweeping away more than 400 houses.

Two people were killed in the 1983 eruption.

Agency officials said a volcano could erupt a few hours after initial temblors are monitored.

The Metropolitan Police Department said it set up a liaison office Monday night to cope with emergency situations.