BANGOR, Maine — A sinkhole that opened up about noon Friday in Norumbega Parkway, a city park between State and Franklin streets that is bordered by the Kenduskeag Stream, was cited as the cause of a machinery mishap.

Bangor Public Works Director Dana Wardwell said Friday night that a piece of heavy machinery — known as a man lift, bucket truck or cherry picker — was in the parkway as part of an inspection of historic Norumbega Hall, the large brick building that houses Eastern Maine Development Corp. and the University of Maine Museum of Art, when the sinkhole appeared and the machine sank into it.

Wardwell said it was not yet clear what caused the hole, which he said is about 15 feet deep and about 4 feet in diameter at its top and larger at the bottom. He said the hole could have resulted from erosion from the Kenduskeag Stream or from the collapse of an old pipe.

Wardwell said the operator of the machine was not injured.

CORRECTION: The park is between State and Franklin streets.

Wardwell, who was still at the scene about 7:30 p.m. Friday despite it being his birthday, said city workers would cover the hole with a metal plate as a temporary safety measure.

The long-term repair will depend on the hole’s cause, he said. If a pipe did collapse, it will be repaired and the hole will be filled. If erosion is found to be the cause, the city will fill the hole with rocks.