The crew on the huge container ship that caused a bridge collapse in Baltimore made a mayday call reporting an on-ship power outage shortly before the impact, possibly averting further tragedy, officials said.

"These people are heroes," Maryland Gov. Wes Moore said. "They saved lives." 

Here's a timeline of the moments before and after the collapse of the Francis Scott Key Bridge:

• 1:24 AM -- Lights flickered aboard the Dali cargo ship
• 1:26 AM -- The Dali abruptly changed course, toward a pillar of the bridge
• 1:27 AM -- Lights aboard the Dali flickered again, then the Dali impacts the bridge
• 1:40 AM -- A 911 call center directed a call to the Baltimore City Fire Department
• 1:50 AM -- The first BCFD unit arrived on scene and reported a complete collapse

Moore said the cargo ship reported losing power and the crew radioed that it was having issues.

The crew dropped anchor as part of safety procedures, but it wasn't enough to stop its inertia, CNN reported, citing officials.

The Key Bridge collapsed around 1:30 a.m. after the Dali cargo ship, which had just left the port, hit the structure.

Moore said at a morning news conference that bridge workers were able to stop vehicle traffic across the Key Bridge before the ship hit it.

Eight construction workers on the bridge fell into the water in the collapse. They were on an overnight state work crew fixing potholes on the bridge.

Six of them remained missing as of late Tuesday morning, according to Paul Wiedefeld, Maryland's transportation secretary. Another two had been accounted for: one in the hospital, one not.

About 50 divers were in the frigid water on Tuesday. They had located three cars, a cement truck and another possible vehicle.

"We have an unspeakable tragedy," Baltimore Mayor Brandon Scott said.

Francis Scott Key Bridge Collapse

The Francis Scott Key Bridge, known locally as the Key Bridge, was opened in 1977 and spans the Patapsco River. It is a vital artery that, along with the Port of Baltimore, is a hub for shipping on the US East Coast.

Shipping in and out of the port is suspended indefinitely.

Jagged remnants of its steel frame were lying across the Dali. An on-ramp now ends abruptly where the fallen span once began.

Officials say it will be a long-term process to rebuild the bridge.