It used to be a vibrant and bustling block teeming with artists, college students and urban eclectics.
"You rarely see a scene of such devastation in the middle of a city like this," Mayor Bill de Blasio told reporters Friday, hours after touring the block where the blast and gas-fed fire leveled three buildings the day before.
Investigators are looking into whether a gas line was "inappropriately accessed" at the building where the explosion left more than 20 people injured -- four critically -- and two more unaccounted for, de Blasio said.
One additional person may be among the missing, NYPD Chief of Detectives Robert Boyce said.
Officials provided a rough timeline of what preliminarily appears to be a "gas-related" explosion.
Gas utility inspectors checking on work in the building's basement left the premises about 30 minutes before the 3:17 p.m. blast.
A contractor and subcontractor at the building met with Consolidated Edison inspectors at 2 p.m. to discuss renovation work, city officials said. The inspectors were looking at piping to introduce gas into the building in the future.
No safety issues were found but the inspectors -- who left the building about 2:45 p.m.-- recommended changes. No gas leaks were detected. There was a second gas service working at the same building, officials said.
At 3 p.m., the owner of a sushi restaurant on the street level called the building owner about the smell of gas, Boyce said. The owner notified the contractor. Roughly 15 minutes later, the contractor and his son were investigating when the explosion occurred.
In a statement, Con Ed said the building was inspected and "records show the work of the building's plumber failed two inspections, including the inspection our personnel conducted (Thursday) afternoon."
"At no time was use of the new service line authorized by Con Edison. That service was locked to ensure that it would not be used. The ground-floor restaurant was being served by its current, smaller gas service line."
De Blasio said first responders and ordinary New Yorkers jumped in with "great acts of kindness ... and bravery."
"This city knows how to handle adversity," he said. "We never welcome it. We know it will come but we know how to handle it. People band together."
An off-duty firefighter, who has already been cited for bravery six times, was in the area and immediately climbed the fire escape in the burning building to look for residents, the mayor said.
A group of bystanders pulled a woman away from one of the collapsing structures.
"Thank God we haven't lost anyone yet, and part of it is because of these extraordinary efforts," de Blasio said.
One of those missing is Nicholas Figueroa, who was at a sushi restaurant during the time of the explosion, according to the New York police sources.
His brother, Neal Figueroa, told CNN that his family is working with authorities in the search. Nicholas failed to show up for work at Bowlmor Lanes in Chelsea on Thursday evening.
"We started calling everywhere," Neal Figueroa said, adding that the woman his brother had lunch with was at a hospital. "We went to every hospital. ... He wasn't there."
Nicholas Figueroa is a "pure soul" who visited animal shelters to walk dogs, his brother said.
"I don't care what my brother is doing as long as he comes home," Neal Figueroa said.
Police confirmed Moises Locon is another man unaccounted for since the blast. NYPD sources say he is an employee at the sushi shop and was reported missing by his brother.
"I saw that young man every day, every single day we had a chat to say 'hello how's business,'" Michael Schumacher, who owns a grocery store near where the explosion occurred, told CNN affiliate WABC.
"Kid worked hard for his family" Schumacher told WABC.
The street-level shop was leveled by the fire and collapse.
The investigation into the cause of the blast is in its early stages.
"It appears to be a gas explosion but there is a lot more we need to learn about," de Blasio said.
The explosion scattered debris, prompted street closures and hurt some who suffered burns in their airways.
Three buildings collapsed and four others damaged by the raging fire. Eleven buildings with more than 140 units were evacuated.
It could take days before investigators can sift through the mounds of rubble, officials said.
Red Cross officials said 83 adults and an infant displaced by the explosion and fire had been moved to hotels.
Con Ed said it had shut off gas to 219 neighborhood customers -- 187 residential and 32 commercial -- while the recovery continues.