An investigation team has been formed to look into the overpass collapse in Seoul on Tuesday, which killed three people, the Republic of Korea's prosecutors said.

"We will work closely with related agencies, including police and labor authorities, to thoroughly investigate the cause of the accident and determine responsibility," the Seoul Western District Prosecutors' Office said in a media notice on Wednesday, according to Yonhap News Agency.

The prosecutors' office also said that it will ensure prompt support for the victims.

The announcement came after the ROK President Lee Jae-myung ordered a comprehensive investigation into the accident on Tuesday and instructed officials to devise preventive measures against a recurrence.

A long section of an aging overpass in central Seoul, built in 1966 and scheduled to be torn down next month, collapsed during demolition work on Tuesday afternoon.

Two senior city public works officials and one outside expert were killed in the accident. Another three workers suffered injuries.

A Seoul city official said the demolition was suspended early on Tuesday for a safety inspection in the afternoon after workers detected signs of subsidence in the structure.

Trains suspended

More than 120 KTX high-speed trains and several regular rail services were suspended or rerouted after the accident as the falling debris affected power lines near Seoul Station, according to the Korea Railroad Corp, or Korail.

The Ministry of Land, Infrastructure and Transport said it plans to restore railway facilities as early as Friday if no further obstacles occur, with normal train operations to resume on the morning of Saturday.

A construction accident investigation committee consisting of 12 external experts will also be formed to determine the cause of the accident and prevent recurrence.

Choi Myung-gi of the Korea Industrial Site Professors Group said the collapse likely resulted from a combination of factors, including inspectors climbing onto the structure and vibrations from train operations below, as the 60-year-old overpass seemed to have very little remaining capacity to bear loads.

"What is even more regrettable is that there is no manual for safety inspection personnel," Choi was quoted as saying by Yonhap. "There are no guidelines whatsoever on how to carry out preventive reinforcement."

While buildings require a demolition plan and supervisor under current laws, Choi said no such system exists for civil structures. He called for reforms to ensure safer demolition work.

In an interview with The Chosun Daily, Gong Ha-sung, professor in the Fire and Disaster Prevention Department at ROK's Woosuk University, said nearby traffic and the lower space should have been controlled first, considering the possibility of further collapse after the structure was first confirmed in the early hours of Tuesday.

In response to questions about the lack of separate fall protection during the safety inspection, the Seoul Metropolitan Government official said wearing safety harnesses or fall protection gear would have required cranes or supports to attach hooks, but such structures were absent at the time.

It was also determined that wearing harnesses was unnecessary, as the safety scaffolding installed could withstand falling concrete.