A power plant under construction in central Connecticut exploded with earthquake force that shook homes as far as 30 miles away on Sunday as workers purged natural gas lines that were to go into use this year. At least five people were killed and more than two dozen injured when a section of the plant collapsed and burned.

Witnesses said the explosion at the Kleen Energy Systems plant in Middletown, Conn., 15 miles south of Hartford, occurred at 11:17 a.m. in a thundering convulsion of flames and smoke seen for miles around and felt as far away as cities and towns on Long Island Sound, 30 miles away.

As towering plumes of dark smoke poured into a dazzling blue sky, scores of ambulances, fire engines, police cars and helicopters streamed to the scene on the west bank of the Connecticut River on the southern outskirts of the city, home of Wesleyan University.

Fire and rescue teams from Middletown, Durham, Portland, Cromwell and other towns converged as crews fought the blaze into the afternoon.