The crew of the cargo ship that struck the Francis Scott Key Bridge in Baltimore lost power and issued a mayday in the moments before the disaster, Maryland Gov. Wes Moore said.

The container ship Dali sent the mayday in time for authorities to stop traffic from entering the bridge, limiting the number of vehicles involved in what officials have called a "mass casualty event."

"We're thankful that between the mayday and the collapse that we had officials who were able to begin to stop the flow of traffic so more cars were not on the bridge," Moore said.

Authorities said a crew of eight construction workers were on the bridge, in addition to any traffic at the time of the collapse.

Search and rescue operations pulled two workers from the water, one in critical condition who was hospitalized. Efforts to locate the other six are ongoing.

Authorities said that sonar had detected cars in the water, which is about 50 feet deep. The temperature was about 47 degrees Fahrenheit before dawn on Tuesday, according to a buoy that collects data for the National Oceanic and Atmospheric Administration.

Moore said an investigation is ongoing to determine how many people were caught in the collapse and plunged into the river.

"But the thing we do know is that many of the vehicles were stopped before they got onto the bridge, which saved lives in a very, very heroic way."

At least they were able to stop traffic.