Officials believe a gas leak prompted the explosion and building collapses.

NEW YORK CITY—An explosion in East Harlem Wednesday morning led to the collapse of two area buildings, according to several news reports. As of Thursday morning, seven people were killed while dozens were injured while at least nine area residents were unaccounted for, GlobeSt.com has learned.

“This is a tragedy of the worst kind,” said Mayor Bill De Blasio at a news conference, because there was no warning. The explosion and fall of the two buildings—at 1644 and 1646 Park Ave., near 116th street—sent debris onto Metro-North Railroad tracks across the street from the site, prompting a shut down of trains into and out of Grand Central Terminal until further notice, according to New York Newsday. A transit spokesman would not speculate on how long it would take to clear the tracks or on whether the shut down would still be in place during Wednesday’s evening rush hour.

GlobeSt.com was unable to ascertain at press time what companies or individuals own the properties. At 9:13 a.m., a report of a gas odor from a resident at 1652 Park Ave. came into Con Edison. Crews were dispatched and arrived just after the explosion, representatives of the utility concern reported on Twitter. The site of the explosion and collapses was reportedly home to the Spanish Christian Church and a piano-repair shop, as well as apartments, reports Bloomberg.com.