Story highlights Gas utility inspectors were at the blast scene an hour before explosion

At least 19 injured, four critically, in major building collapse in New York

No one was trapped in the collapses

New York (CNN) Inspectors from New York's gas utility were at a building in Manhattan's East Village on Thursday a little more than an hour before a fiery blast injured at least 19 people, at least four critically, leveled the structure and a neighboring one, officials said.

The explosion appeared to be "gas-related," Mayor Bill de Blasio said, adding there were no reports of gas leaks beforehand.

The cause is under investigation.

Consolidated Edison inspectors were at the Second Avenue building "evaluating the meter installation for a new service ... to the building," utility President Craig Ivey told reporters. There was a second gas service in operation at the same building.

The installation of the new meter "did not pass our inspection at that time, so it meant it wasn't ready for gas to be introduced," Ivey said. Con Edison said in a statement that a survey Wednesday of gas mains on the block found no leaks.

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