"People of Baltimore, we're with you," he said, as he added the search and rescue operation was a "top priority".

Wes Moore, governor of Baltimore, and Paul Wiedefeld, secretary of the Maryland Transport Authority, have said those missing are believed to be construction workers who were on the bridge fixing potholes.

Two people were rescued from the water with one of them described as being in a "very serious condition" in hospital.

The other was not injured.

Meanwhile, the US president said the federal government will cover the "full cost" of rebuilding the bridge. He said it may emerge a private company was responsible for the disaster, but his government is "not going to wait" to begin the rebuilding process.

Mr Biden told reporters at the White House: "It's my intention that the federal government will pay for the entire cost of reconstructing that bridge and I expect Congress to support my effort."

Baltimore bridge latest: Follow live updates

Mr Biden continued: "Everything so far indicates that this was a terrible accident. At this time have we no other indication, no other reason to believe there's any intentional act here.

"Personnel on board the ship were able to alert the Maryland Department of Transportation that they had lost control of their vessel."

The president added that this meant local authorities were able to close the bridge before it was struck which "undoubtedly saved lives".

He continued: "Our prayers are with everyone involved in this terrible accident and all the families (affected), especially those waiting for news of their loved one right now. I know every minute in that circumstance feels like a lifetime."

Read more:
'Huge implications' as bridge collapses forces port to close
Baltimore ship's four critical minutes before collision
Two possible causes for the disaster

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The US president said the search and rescue operation remains the "top priority" but authorities will be working to get the port open again as soon as possible.

The Port of Baltimore, which is accessed or departed by going underneath the bridge, is one of the US' largest shipping hubs.

Mr Biden said 15,000 jobs depend on the port.

"We're going to do everything we can to protect those jobs," he added.

He continued: "I've directed my team to move heaven and earth to reopen the port and rebuild the bridge as soon as humanly possible."

The 1.6-mile long Francis Scott Key Bridge collapsed into the Patapsco River after it was hit by a 289m-long cargo ship at 1.30am local time (5.30am UK time) on Tuesday.

Six people remain unaccounted for after dramatic footage showed vehicles falling from the structure as the road surface and steel beams crashed into the water.

Baltimore fire department's communications chief Kevin Cartwright has said there were multiple vehicles on the bridge when it was struck by the ship, one of which was the size of a tractor trailer.

CCTV and marine tracking data shows the ship, known as the Dali, lost power, adjusted its course and started smoking about 60 seconds before it hit the bridge.

According to the timings on the CCTV, the vessel hit the structure at 1.28:44am - with the bridge collapsing four seconds later.

All 22 crew members on board the ship, including the two pilots, have been accounted for and there were no reports of injuries.

The National Transportation Safety Board (NTSB) said in a news conference that its investigators will not board the Dali on Tuesday.

The authority's chair Jennifer Homendy said the decision has been made to give "some time to the search and recovery effort".

"We did not want to interfere," she added.

Ms Homendy explains the NTSB will be able to provide more information in the "coming days", and voyager data recorder information will be "critical".

She says the NTSB will be leading the investigation and the Coast Guard will support it.

The same ship was previously involved in a minor incident when it hit a quay at the Port of Antwerp in Belgium in 2016, according to Vessel Finder and maritime accident site Shipwrecklog.

The vessel was reportedly damaged in the incident, but there were no injuries or pollution issues reported.

Meanwhile, Mayor of Baltimore, Brandon Scott has declared a local state of emergency which will be in place for the next 30 days as the search for the missing continues.

The National Transportation Safety Board is also conducting an investigation into the incident.

The Singapore-flagged ship was headed to Colombo in Sri Lanka at the time of the collision.

It was chartered by Danish shipping company Maersk, which said it was "horrified by what has happened". It said its thoughts were with everyone affected.

The Port of Baltimore is the 11th largest in the US, meaning its closure will cause knock-on effects for the industry.

Built in 1977, the Francis Scott Key Bridge is one of the longest continuous truss bridges in the world, according to the National Steel Bridge Alliance.

It was named after the writer of The Star-Spangled Banner, the national anthem of the US, which was penned after a War of 1812 US-UK battle in Baltimore harbour.

Tune into a special edition of The World with Yalda Hakim on Sky News tonight at 9pm.