Authorities say a woman was killed after the Boston drawbridge she was walking on started to go up and she was crushed between the bridge plates when the operator lowered it to help her.

Investigators call the death on the Meridian Street Bridge just after noon on Tuesday an accident. The victim was not identified.

Police said the bridge operator was not aware that the woman was on the bridge when it was raised to allow a boat to pass. The bridge operator heard a scream and lowered the bridge, but the woman became trapped and suffered massive trauma. She was pronounced dead at the scene.

Police said the distraught bridge operator was taken to a hospital for evaluation.

The bridge spans the Chelsea River between East Boston and Chelsea.