Rescue workers are battling "difficult" conditions as they race to save drivers and workers from chilly waters after the overnight collapse of Baltimore's Francis Scott Key Bridge, Baltimore County Executive Johnny Olszewski said Tuesday. 

"Our focus has very much been on the search and rescue and the search and recovery efforts here in this situation," Olszewski told CNN. "The conditions are difficult."

The water is cold and the currents are strong, he said.

Officials estimate that seven people went into the water including workers doing construction maintenance on the bridge when the Dali cargo ship hit the structure shortly after leaving port around 1:30 a.m.

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

The Dali's owner confirmed its ship was involved in the incident, the New York Times reported.

"All crew members, including the two pilots, have been accounted for, and there are no reports of any injuries. There has also been no pollution," the firm said in a statement obtained by the shipping news outlet TradeWinds.

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 U.S. East Coast.

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