OLVESTON, Montserrat – The volcano that destroyed Montserrat’s capital in 1997 shot a cloud of ash more than five miles into the sky yesterday, and one of the island’s chief scientists said the blast was “a warning call.”

The government has advised about 50 families on the northwestern side of the volcano’s base that their homes were at risk from flows of blistering gas and debris if the dome collapses. Gov. Deborah Barnes Jones said she would sign an evacuation order yesterday making it illegal for people to remain in the area.

The blast, accompanied by increased seismic rumbling, released gases and steam from inside a lava dome that has grown rapidly over the last week, said Dr. Vicky Hards, director of the Montserrat Volcano Observatory.

“I think it was a warning call … of what it can do,” Hards said.

The explosion around sunrise also sent a flow of volcanic material cascading two miles down the northwest flank, but did not immediately threaten any of the British Caribbean island’s 5,000 inhabitants, Hards said. Sirens alerted people to listen to the radio for updates.

“People in the affected area know who they are and should work urgently on packing up and arranging for alternative accommodations,” Barnes Jones said in a radio address.