19 injured as apparent gas explosion rocks 5-story building in New York

NEW YORK --  An explosion rocked a heavily traveled section of Manhattan's East Village on Thursday, injuring 19 people and leveling parts of a building, authorities said.

At least four of the injured in the seven-alarm fire were in critical condition, a fire department spokesman said.

Inspectors from New York's gas utility were on the scene of a building explosion in Manhattan's East Village on Thursday about an hour before the blast occurred, Mayor Bill de Blasio said.

The inspectors, who found gas work at the building "unacceptable" and recommended changes, are now talking to investigators.

The fiery blast appeared to be a "gas-related explosion," de Blasio said.

Towering flames and plumes of black smoke at one point rose from the building, which includes both apartments and businesses. Emergency personnel could be seen taking the injured away on stretchers.

At least 250 firefighters were on the scene.

The collapsed first floor houses a Japanese restaurant; the building next door, with a shop specializing in French fries on the street level, was ablaze and, in later images, appeared to have completely collapsed.

The official FDNY Twitter account described it as a "major building collapse."

The explosion comes just over a year after two buildings in Harlem collapsed after a gas leak last March, killing eight people and injuring dozens. The buildings were served by a 127-year-old gas main.

After the 2014 incident, experts warned that many U.S. utilities were struggling to maintain or replace antiquated, hard-to-reach and leaky gas mains in older urban areas. The most vulnerable mains are made of cast iron or steel.

A day before the Harlem explosion, the New York-based Center for an Urban Future said in a report that New York's aging infrastructure "could wreak havoc on the city's economy and quality of life." An estimated $47.3 billion would have to be devoted for repairs to maintain safety.

The average age of New York City's 6,300 miles of gas mains is 56 years old, wrote the report's author, Adam Forman.

CNN and PIX11 New York contributed to this story.