Four women and three men have been found dead at the scene of Wednesday's building collapse in East Harlem, an NYPD spokesman has told the AFP news agency.
Three of the women were aged 21, 44 and 67. Police say all the dead were recovered at the scene and the number still unaccounted for is being verified.
In total, 68 people were injured in the explosion, including those treated by first responders, police said on Thursday. Hospital officials had put the figure at 63.
The Mexican foreign ministry said two women among the dead were Mexicans, along with one of those injured.
The explosion sparked inevitable reminders for some New Yorkers of the 9/11 terror attacks in 2001 that brought down the Twin Towers.
Other witnesses said it felt like an earthquake, describing how they were knocked to the floor.
Mayor Bill de Blasio called the incident "a tragedy of the worst kind" because the smell of gas was detected "but there was no indication in time to save people".
Where the apartment buildings once stood are piles of twisted metal, thick white smoke and dusty rubble - a scene of utter devastation that witnesses likened to a war zone.
There were 15 apartments in the two buildings that collapsed, de Blasio told reporters.
Jazzmen Arzuaga, 30, said she was at work when her wife rang to tell her what had happened.
"She called me and told me 'Oh my God, you need to come home now, it's like World War II, people are dying, there was an explosion.' I just literally ran," she said.
The couple live across the street from the blast site.
Arzuaga's wife Jay Virgo, also 30, said she was lying in bed when the blast threw her to the floor.
"There was glass everywhere, huge pieces of glass. It just looked crazy," she said.
Firefighters took hours on Wednesday to extinguish the heavy fire at 116th Street and Park Avenue, a mainly Latino community in northern Manhattan.
Around 15 minutes before the blast, energy company Con Edison received a call from an adjoining building alerting maintenance staff to the smell of gas.
It was the first deadly disaster of its kind to strike the city of eight million since de Blasio took office in January and may raise concerns about safety in less affluent neighbourhoods.
"There is a tremendous amount of anxiety but suffice it to say that every effort is being expended to locate each and every one of these (missing) individuals," the mayor said.