Union, NJ – John Cummins, New York Times – An explosion from a leak in a gas line destroyed two homes and badly damaged two others here on Sunday morning, authorities said. A couple who lived in one home were critically injured, and their daughter was in serious condition.

Edward Sanchez, 18, said he was watching television shortly after 3 a.m. when he heard the blast and saw flames shooting from a nearby house, at 744 Lehigh Avenue, a thoroughfare near Kean University with modest single-family homes on one side and warehouses on the other.

Mr. Sanchez said he immediately smelled gas and woke his mother and sister. Together they fled their house, at 752 Lehigh, and once outside, saw their neighbors running from 744 Lehigh, which was partially collapsed and engulfed in flames.

Mr. Sanchez said the fire quickly spread to the house next door, 748 Lehigh, which firefighters quickly evacuated. Then a second, larger explosion rocked the neighborhood, sending debris flying up to 300 feet. The house at 748 burst into flames and exploded.

”It literally blew the roof off of the house and flipped it upside down,” said the chief of the Union Fire Department, Frederic Fretz.

Firefighters got the fire under control a few hours later. The explosions also severely damaged Mr. Sanchez’s house and the one at 740 Lehigh, which was unoccupied.

The couple who were badly injured, Charmaine Thomas, 40, and her husband, Ferdinand, live at 744 Lehigh Avenue, which also was destroyed. Both were listed in critical condition at St. Barnabas Medical Center in Livingston. Mrs. Thomas had second- and third-degree burns to her back, face and right arm.

Her husband had cuts, bruising and burns after he jumped from the second story with the couple’s daughter, Samantha, to escape the flames. The daughter was listed in serious condition with cuts and smoke inhalation. Fire officials said that several residents, including the Thomas family, told firefighters that shortly before the blasts, they had noticed a strong smell of natural gas inside their homes.

”The area was rich with gas,” Chief Fretz said. ”These explosions are not totally uncommon, but we were fortunate that there weren’t more injuries.”

Chief Fretz said two firefighters suffered were slightly injured while fighting the blasts, which sent thick black smoke into the frigid sky. Officials from Elizabethtown Gas clamped the gas line in the neighborhood and shut off service to seven homes and four businesses, said Martha J. Monfried, a utility spokeswoman. By Sunday afternoon, gas had been restored to all except the four damaged homes as state and county investigators combed the scene for evidence.