A major search and rescue effort is underway in the US city of Balitmore following a horror bridge collapse.

An out-of-control cargo ship smashed into a pylon of the 2.57-kilometre Key Bridge just before 1.30am local time on Tuesday, causing the bridge to tumble into the Patapsco River below.

Authorities have confirmed the ship managed to issue a May Day call after losing power, giving officers some time to stop as many cars as they could from driving onto the bridge.

However, eight people were already on the bridge at the time of the collapse.

Two people, including one who was taken to hospital in a serious condition, were pulled from the river.

However, the six others, believed to be road workers, remain unaccounted for with a mass air, land, and sea search currently underway.

“There is not a single resource that we will hold off on deploying,” Maryland governor Wes Moore said.

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“This is very much still a search and rescue mission, we are still actively looking for survivors”.

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More to come.

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