WINTHROP, Maine — A fire ripped through the Winthrop Post Office Tuesday morning, sending heavy smoke into the air and shutting down Main Street for a few hours.

Fire and postal officials said the fire started just before 9 a.m. when a clerk inside noticed smoke coming from a ceiling tile and got everyone out of the building.

No one was injured, but it took just minutes for the flames to spread and engulf the roof.

Chief Dan Brooks of the Winthrop Fire Department said the fire was still under investigation, but that heating equipment in the ceiling may have malfunctioned.

The roof collapsed and everything inside, including the mail, was destroyed.

“I don’t think much mail is gone out yet this morning and anything that’s in there is pretty much ruined,” Brooks said. “So I don’t believe there will be any mail deliveries. And I don’t know what they’re doing overall. I’m sure they’re working on a plan.”

U.S. Postal Inspectors said later that they were taking over the fire investigation and that there was no timetable for resuming operations at the location.

In addition to retail services, the office served 545 Post Office Box holders and was home base for five delivery routes.

Deliveries were expected to resume Wednesday and P.O. Box holders were to be served temporarily out of the Manchester Post Office, also beginning Wednesday.

Tuesday afternoon, postal officials were awaiting clearance to enter the building and determine the extent of any damage to mail and parcels.

Customers were being advised to contact anyone they were expecting mail from to determine its status. Anyone with tracking data indicating that a package was at the facility Tuesday morning can go to to file a claim.