(AP) - Someone may have improperly tapped a gas line before an explosion that leveled three apartment buildings and injured nearly two dozen people, Mayor Bill de Blasio said Friday as firefighters soaked the still-smoldering buildings and police searched for at least two missing people.

"There is a possibility here that the gas line was inappropriately accessed internally" by people in one of the destroyed buildings, but officials need to get access to its basement to explore it further, said de Blasio, who wouldn't say more about why officials believe that's a possibility.

The number of people injured in Thursday's blast rose from 19 to 22, with four critically injured. Police were searching for at least two people: Nicholas Figueroa, a bowling alley worker who had been on a date at a sushi restaurant in the building where the destruction was centered, and Moises Lucon, a worker there. Authorities also were exploring whether a third person might be unaccounted for, Chief of Detectives Robert Boyce said.

Preliminary evidence suggests an explosion amid plumbing and gas work inside the building was to blame.

Inspectors with utility Consolidated Edison had been to the East Village building to check on ongoing work to upgrade gas service. The utility said the work didn't pass inspection, so gas wasn't introduced to the line, and inspectors gave instructions and left at around 2:45 p.m. Con Ed said inspectors didn't smell any gas.

But at around 3 p.m., the sushi restaurant owner smelled gas and called the landlord, who then called a general contractor, Boyce said. No one called 911 or Con Ed, however, de Blasio said.

The contractor, Dilber Kukic, and the owner's son went into the basement and opened a door, and then the explosion happened, burning their faces, Boyce said.

The building had an existing gas line intended to serve the sushi restaurant; the work underway was to put in a bigger line to serve the entire building, Con Ed President Craig Ivey said. As for whether the apartments were getting gas from the existing line, "That's a great question," he said.

"We'll have to find out, through the investigation, what's going on there," he said.

Figueroa graduated from Buffalo State College in December with a bachelor's degree in criminal justice and a minor in intelligence analysis. He has been working at Bowlmor Chelsea Piers for the past few months as a front desk attendant and laser tag attendant.

On Thursday night, Tyler Figueroa said his brother and his date were paying for their meal when the blast occurred. The date, who is in the hospital, remembers only stumbling outside before losing consciousness, Tyler Figueroa said.

"I just pray my brother shows up," he said.

Efforts to reach Lucon's family weren't immediately successful.

On Friday, firefighters used high-powered water towers to douse the wreckage, a giant wave of crumbled brick, twisted metal, splintered wood and bits of residents' belongings. Rubble was still strewn across parked cars, and a menu from the sushi restaurant and other debris were scattered across the surrounding streets.

The blast echoed through the city's arts community, destroying "Sopranos" actress Drea de Matteo's apartment - she posted photos on Instagram of "a hole where my NYC home of the last 22 years once stood" - and spurring the cancellation of five performances of the propulsive show "Stomp," which is at a theater near the site.

Kukic, who's facing unrelated charges of bribing an undercover investigator posing as a housing inspector, declined through his lawyer to comment on the circumstances surrounding the explosion. City records show Kukic got a permit last June for plumbing, flooring, removing partition walls and other work at the building.

Kukic was treated and released from a hospital, said his lawyer, Mark Bederow.

Kukic is a relatively minor player in a 50-person bribery case authorities unveiled last month. He is accused of paying $600 to try to get housing violations dismissed at two upper Manhattan properties he owned. He has pleaded not guilty.

The blast happened a little over a year after a gas explosion in a building in East Harlem killed eight people and injured about 50. A gas leak was reported shortly before that blast.