Authorities say the five victims are a couple in their 70s, a 4-month-old boy, a 16-year-old girl and one of the children's parents. The victims are from two families who lived in the two townhouses that were destroyed by the blast.
The explosion rocked the neighborhood at 10:45 p.m. on Wednesday, touching off fires that blazed into the early-morning hours as firefighters combed through snow and ice to stop an underground pipeline from feeding the flames.
Authorities said at least six homes will not be salvageable and two homes were entirely leveled. Forty-seven homes and ten businesses were damaged by the explosion, fire or ice.
Utility workers inspected the area the day before the explosion and detected no leaks. The pipe that fed the explosion was installed in 1928 and Ed Pawlowski, the mayor of Allentown, said old and dangerous pipes run under many cities.
"Lines built over 150 years ago are still servicing a lot of these buildings today," Pawlowski said. "When you have constant thawing and freezing you're going to have problems ... and lead to disasters like this."
Utility workers were called in to assist and get the gas lines shut off after the explosion on the 500 block of North 13th Street. Snow piles and ice hampered firefighters as they attempted to put out the flames. UGI Corporation, the local gas utility, was unable to shut off the gas until 3:45 a.m.
The magnitude of the explosion and flames forced the evacuation of hundreds of residents. The cause of the explosion is being investigated.
"I think we are going under the assumption that it is a gas explosion, but it has not been confirmed to be the case," Joseph Swope, a UGI spokesman told the Morning Call.
He said the 12-inch low pressure main involved in the incident hadn't had any history of leaks.
The powerful blast sent a computer monitor crashing into the home of one person in the neighborhood, according to The Associated Press.
"I thought we were under attack," Antonio Arroyo told the AP. "What I saw, I couldn't believe." Arroyo and his wife sought refuge in a shelter after the explosion destroyed their home. The couple expects to return to their home to see what can be salvaged but every keepsake they own may be lost.
"This is a real tragedy," Mayor Ed Pawlowski told the Morning Call. "Our thoughts and prayers are with the families."
The tragedy follows another explosion that rocked the West Coast last year.
The explosion that leveled a San Bruno, California, neighborhood in September sent flames 300 feet into the air after a ruptured natural gas pipeline -- in that case, one belonging to the Pacific Gas & Electric Company.
San Bruno's fire and explosion destroyed 53 homes and damaged 120 more. It killed seven and injured more than 50. "The central ball of fire," said a reporter for the San Francisco Chronicle, "raged past nightfall before abating. By then, houses on several blocks and thick stands of trees were engulfed in flames."
The death toll wasn't the worst in pipeline history. An incident 10 years ago in Carlsbad, New Mexico, killed 12. Pipeline blasts in the past five years have killed 60 and injured 230.
Though roughly half these incidents were the fault of parties other than utilities (builders or cable companies that accidentally dug into underground pipes), pipeline operators dug into their own pipes in at least two dozen cases. Other incidents for which they were responsible involved corrosion, faulty equipment and operator error.
The San Bruno incident was caused by a pipe that ruptured because of regular changes in gas pressure, according to federal investigators.
The age of a pipeline matters less than inspection and maintenance, said Carl Weier, head of the Pipeline Safety Trust, a government-financed watchdog group. "Most of the pipelines in this country are 40 to 50 years old. If properly maintained, they don't present a danger."
But even a new pipeline, he said, will fail if not well-inspected and maintained. Corrosion caused the Carlsbad event, according to inspectors who examined the wreckage. Weier said the danger of future explosions could be defused by better and more frequent inspection, especially in rural areas, where pipelines get a thorough going-over only once every seven years.
The Associated Press contributed to this story.