The ship’s mayday call prompted officials to stop traffic to the bridge.

A mayday call enabled officials to stop traffic at both ends of Baltimore’s Francis Scott Key Bridge and try to evacuate people from the span before it collapsed on Tuesday, according to several federal and Maryland officials.

The crew of the large container ship leaving the Port of Baltimore told Harbor Control that they had lost power and propulsion, the officials said.

The ship “drifted into the bridge,” said Chris Van Hollen, a Democrat and Maryland’s junior senator. “Before it hit the bridge, it issued a mayday warning, which did give folks enough time to stop some of the traffic crossing the bridge.”

Mr. Van Hollen said that the investigation was still in its early stages but added that early indications suggested that because of the closure, no traffic was crossing the bridge during the collapse. He said vehicles used by a road crew fixing potholes had been parked on the bridge and appear to have been plunged into the water.

Mr. Van Hollen and a U.S. official briefed on the incident said it was not clear how much time had elapsed between the mayday call and the ship’s crash into the bridge.

Shortly after the crash, radio traffic from emergency workers suggested that the crew was also struggling to steer the ship, according to audio published by Broadcastify.