NEW YORK, March 12 -- A powerful explosion leveled two residential buildings in New York's East Harlem neighborhood on Wednesday morning, killing two people and wounding at least 22 others. More than 12 people remained missing, authorities said.

The blast struck a building at 116th Street and Park Avenue in Upper Manhattan at about 9:30 a.m. local time (1330 GMT), blowing out windows in surrounding buildings and sending debris crashing down onto nearby streets.

Two five-story residential buildings next door to each other collapsed in the incident, with one essentially gone from the blast.

At least 12 people remained missing so far, and two of the wounded had life-threatening injuries, fire officials said, indicating that the death toll could rise further.

Hours after the explosion, smoke and ashes from the explosion can still be seen pouring into the neighborhood where about 250 firefighters were battling to extinguish heavy blaze.

Preliminary investigation suggested that the only warning came before the blast is a call about a gas leak.

Utility company Con Edison said it received the call from a resident in an adjacent building about 15 minutes before the explosion. The company said it sent two crews to the scene after the call, but they arrived just after the explosion.

New York Mayor Bill de Blasio said that "the explosion was based on a gas leak. The impact affected buildings around the two that were destroyed, very heavy impacts on the surrounding buildings. A heavy fire has ensued as well."

"This is a tragedy of the worst kind because there was no indication in time to save people," he told reporters at the scene shortly after noon.

"There will be a search through the rubbles of the building as soon as the fire is put out looking for those who are missing," de Blasio said.

"Hopefully, again, we will find that some of those individuals are somewhere else in the city and just had not yet been located on their cellphones," he added.

About half an hour after the explosion, police cordoned off a two-block radius. At least four New York Police Department helicopters can be seen patrolling in the air.

Meanwhile, Metro-North Railroad service in and out of New York City's Grand Central Terminal was suspended as debris from the buildings were thrown onto the elevated train tracks on 116th Street and Park Avenue.

Workers of Metropolitan Transportation Authority (MTA) were racing to remove debris scattered along the tracks, an MTA spokesman said, giving no clear time when traffic into the Grand Central Terminal would resume.

In the immediate aftermath, witnesses described a chaotic scene with people in panic and a serious fire spewing out thick smoke.

Gregory Garcia, who was just a block away from the scene before the explosion, told Xinhua that he was shocked by a huge explosion. Everyone was running in panic unsure what had happened, he said.

The two collapsed five-story buildings had a piano store and a Spanish Christian Church on the ground floor and apartments on the upper, Garcia said.

Kevin Kim, manager of the Total Beauty Supply store located at the corner of the 116th street, told Xinhua he heard a "loud explosion" while working inside his store, and felt the ground was "shaking".

"I rushed outside and saw smoke rising from across the street. Minutes later, lots of fire engines and ambulances raced to the collapsed buildings," he said.