The badly burned body of an unidentified woman was also discovered outside one of the homes, on the hood of a car.
A female resident of that unit remained unaccounted for Tuesday night, and officials said the condition of the body meant an identification would have to wait for an autopsy.
That unit appeared to have been the epicenter of the explosion, though officials were hesitant to label it such because of the widespread nature of the blast.
"It's like somebody dropped a bomb. I don't have a guess where it started," said Lt. Ronald P. Lunetta of the Ewing Police Department. "I've never seen anything like it."
It was not clear Wednesday what set off the blast. Workers earlier had damaged a gas line, apparently leading to a gas leak.
A spokesman for Henkels & McCoy, a Blue Bell, Pa.-based contractor, confirmed it had been doing utility service work for a customer and was "fully cooperating with the authorities on site about the investigation."
Lunetta said the Henkels & McCoy crew was "digging in that area" to address a power problem when a worker "felt that they had struck something."
"Obviously, it was a gas line," he said. "At that point, they retreated and tried to make contact with their people and also Public Service" Electric & Gas Co.
That report came around 11:45 a.m., a PSE&G official said at an afternoon news conference. Its workers arrived just before noon.
The gas line had been damaged, causing a leak with the reported odor of gas in the air, Michael Gaffney, a PSE&G official, said at a press conferences.
Gaffney said the source of the ignition was still under investigation.
"PSE&G gas crews had just arrived on scene to investigate when there was an ignition," according to a statement.
Lunetta said the first 911 call for the explosion came in at 12:51 p.m.
Officials said no one was evacuated in the approximately one-hour span between PSE&G workers' arrival and the explosion.
Asked whether people should have been evacuated, Lunetta said investigators had been "getting conflicting stories right now" and would need more clarity.
"There's too much up in the air, I don't want to speculate," he said.
The explosion shook dozens of homes and apartments in the area. The force hurled one woman from the third step of a ladder to the floor in a neighboring complex. With Trenton-Mercer Airport a mile away, some residents said they feared a plane had crashed.
Firefighters combed through the destruction, marking a pink "X" on damaged homes they had explored. At some, blinds hung out of broken windows and garages were dented as if struck by boulders.
Capital Health Regional Medical Center in Trenton treated five patients, releasing one. Two others were taken to Capital Health Medical Center-Hopewell and released.
The Trenton hospital initially said one patient was in critical condition, but later said that classification was upgraded after further examination.
"The most severe injuries were lower-extremity fractures," said Louis F. D'Amelio, the director of the hospital system's trauma services. Injuries included concussions, soft-tissue blast injuries, leg fractures, and some shrapnel injuries, he said.
"None of them would be described as life-threatening, and overall I'd consider them minor to moderate if you look across the whole spectrum of patients," said D'Amelio, who is also chair of the hospital's surgery department.
The hospitals had not treated patients for burn injuries, he said, because the victims had been "thrown a distance. Although they were subject to the force of the explosion, they weren't subject to fire."
The American Red Cross North Jersey Region was at the West Trenton firehouse Tuesday night, offering to help arrange lodging for families in need.
Josh Forst, a 21-year-old who lives about a quarter of a mile from the development, said he was watching TV when the explosion rattled the neighborhood.
"I heard a loud bang and the house shook really violently," he said. "We thought a tree fell initially."
Said Jim Devlin, 58, who lives across a creek to the rear of the home that exploded, "It was unbelievable how it sounded and felt, pretty amazing the power of that stuff."
Bert Steinmann, mayor of Ewing, said "words can't really explain it. It's just very devastating to see that happen."