Police believe a handful of people remained unaccounted for.
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More than 60 people were injured after the devastating blast sent debris flying through the air on Wednesday.
Residents were said to have complained recently about “unbearable” gas smells.
Mayor Bill de Blasio, who rushed to the scene in Upper Manhattan, said preliminary information showed the explosion was caused by a gas leak.
A fire at the site of the blast on Park Avenue and 116th Street hampered the initial search and a sinkhole created by a broken water main caused further difficulties.
But firefighters worked through the night, as temperatures dropped to near freezing, to sift through the rubble, using a bulldozer to help clear the site.
Rescue workers pulled three bodies out of the debris in the early hours of Thursday morning, and a seventh death was confirmed just before 12:00 GMT (08:00 local time).
No details have yet been given of the eighth victim.
Rescuers are now about halfway through clearing the rubble.
“This is a difficult job, a challenging job,” Fire Department spokesman Jim Long said. He added that it was “a very terrible and traumatic scene”.
“We are continuing rescue operations hoping to find others still alive,” Mr de Blasio said on Thursday.
The blast shattered windows a block away and rained debris on to nearby railway lines, which closed Grand Central station for several hours on Wednesday. Source.