A bridge in the US city of Baltimore has snapped and collapsed after a ship collided with one of its support columns. Rescuers are searching the water for survivors and the state’s governor has declared a state of emergency.

Joe Biden has said search and rescue efforts remain a “top priority”, as six people are still missing. The president added there was no evidence the collapse of the bridge was intentional, calling it “a terrible accident”.

Here is what we know about the bridge, the ship and the port.

The bridge

Baltimore’s 1.6-mile (2.57km) Francis Scott Key Bridge was built out of steel and opened in 1977. With four lanes, the bridge is part of Interstate 695 and served as a major route along the ring road that encircles the city in the US state of Maryland.

It is named after the author of the American national anthem, The Star-Spangled Banner. The Maryland governor, Wes Moore, said the bridge had been “fully up to code” before Tuesday’s collision and collapse, indicating it met safety standards.

Live video posted on YouTube showed the ship ploughing into the bridge in darkness, with its main section collapsing into the Patapsco River below.

Several vehicles fell into the water, and officials said eight construction workers assisting with a project fell off. Six people remained unaccounted for.

One official said that sonar had detected cars in the water, which is about 50ft (15 metres) deep.

The National Transportation Safety Board is dispatching a team to investigate the disastrous collapse. Andrew Barr, an expert in civil and structural engineering at the University of Sheffield, said: “The video doesn’t show any obvious structural deficiencies with the bridge, but it will not have been designed to survive a head-on collision with such a large vessel.”

The ship

Ship-tracking data showed a Singapore-flagged container ship, the Dali, at the location of the bridge where the accident occurred at about 1.30am ET (0530 GMT) on Tuesday.

The Dali, a 290-metre (948ft) cargo vessel, left Baltimore at 1am and was headed for the Sri Lankan capital, Colombo, according to the maritime data platform MarineTraffic. The shipping company Maersk said it had chartered the vessel.

The Maritime and Port Authority of Singapore (MPA) confirmed that the vessel was registered in Singapore and said the agency was coordinating with the US Coast Guard and the ship’s management company to help. It also said it would investigate the incident itself.

Moore said the ship had lost power around the time it hit the bridge and the vessel’s crew had issued a “mayday” radio call. The ship then appeared to catch fire as part of the bridge collapsed over it, sending plumes of thick, black smoke into the air.

The shipping company Maersk said that it chartered the container ship in Baltimore, with the operator named as Synergy Marine Group. Maersk confirmed that there were 22 crew, and said they were all Indian. None of them were Maersk crew or personnel.

Reuters cited the manager of the ship, Synergy Marine Group, as saying the crew, including the two pilots, had been accounted for and there were no reports of injuries onboard.

Maersk added that there were 4,679 containers on board, roughly half of its 10,000 capacity.

The same vessel was also involved in a collision in 2016 in Antwerp, Belgium, according to VesselFinder and the maritime incident archive Shipwrecklog. At the time, the stern scraped the side of the quay, significantly damaging several metres of the hull. There were reportedly no injuries or adverse pollution and the weather was reported to be fine at the time. The incident was reportedly blamed on the ship’s master and pilot onboard.

The port

The harbour is one of the busiest in the country and an important hub for shipping on the US east coast, especially in transporting road vehicles. It also handles farming, construction machinery and coal, according to a Maryland government website.

Port traffic was suspended until further notice after the bridge collapse.

Agencies contributed to this report