At least four people died and six were injured on Tuesday after a collapse at a highway construction site in an area south of the South Korean capital, Seoul, fire authorities said.

The accident took place at 9:49 a.m. (0049 GMT) in Anseong, about 70 km (43.5 miles) from Seoul, when five 50 metre (164 ft) concrete structures supporting the highway bridge collapsed one after another after being hoisted into place by a crane, the Yonhap News Agency reported.

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Ko Kyung-man, an Anseong fire official, said that four people had died, including two Chinese nationals, and six were injured, including five who were in a critical condition. The five also included one Chinese citizen.

"They were working to install a deck on the bridge," Ko told a televised briefing. "All of the 10 were up on the deck ... and fell from both sides when it collapsed."

Broadcaster YTN aired dramatic footage showing a deck of a towering bridge collapsing at the site.

Rescue workers at the site were seen examining twisted metal struts and fractured concrete slabs below the columns of the highway bridge.

Acting President Choi Sang-mok called to mobilise all available personnel and resources to rescue any missing people and to ensure safety measures to prevent further damage, his office said.

The National Fire Agency said that it has mobilised three helicopters and nearly 150 officials for the search and rescue operation, and the Transport Ministry said it has dispatched a team of officials to the scene.

Deadly accidents continue to regularly occur at industrial sites in South Korea, which introduced a law in 2022 to address safety lapses and punish company management if a worker is killed on the job.

Earlier in February, six people died in a fire in a hotel construction site in the port city of Busan, with around 100 people evacuated including 14 workers plucked to safety by a helicopter after they had taken refuge on a rooftop.

In June last year, a fire at a lithium battery factory that authorities blamed on quality control failures and inadequate safety training killed 23 workers.

Data released in March by South Korea's labour ministry showed that 598 industrial workers died in 2023, with the construction sector accounting for nearly half, or 303, though the total death toll was down from 644 in 2022.