An apparent steam explosion in a maintenance building at a US veterans’ hospital has killed two people and a third is missing, officials said.

“We received a report this morning that an explosion occurred at the West Haven campus of the VA Connecticut Healthcare System that resulted in two deaths in a non-patient care area,” Veterans Affairs secretary Robert Wilkie said in a statement.

“Neither of the victims were VA patients and patient care was not affected. Emergency personnel are on the scene,” the statement said.

“Our prayers are with the families of the victims of this explosion.”

Max Reiss, a spokesman for state governor Ned Lamont, said a third person was missing.

One of the people who died was a VA employee and the other was a contractor, said senator Richard Blumenthal.

“This kind of explosion may have been the result of a mechanical failure or a mistake on the part of someone at the VA. We have no firm facts as yet,” he said.

The contractor who died worked for Mulvaney Mechanical, based in Danbury, Connecticut, said company vice president Charles Brough. He said he did not have information about the work being done, and the company did not release the contractor’s name.

West Haven firefighters described it as a “steam explosion” at a facilities building a short distance from the hospital, their union said in a Facebook post.

State and federal investigators responded, said Brian Foley, a senior aide to state public safety commissioner James Rovella.

He cited “an explosion-type incident” with “serious injuries”.

The area of the campus where the blast happened was taped off on Friday morning, but people were being allowed to enter and exit the main hospital building.

The federal Occupational Safety and Health Administration is looking into what happened, spokesman Jim Lally said.