Seoul, Dec 13 : The last missing worker in a library construction site accident was found dead Saturday, leaving the total death toll at four in the fatal collapse incident that occurred two days ago.

The body of the 58-year-old worker, identified by his surname Kim, was discovered at around 11:20 am, officials said, bringing the death toll from Thursday's accident to four.

Earlier in the day, authorities found the body of another worker, surnamed Ko, at around 1:03 am. Two other workers died on Thursday, the day the accident occurred.

The four victims were identified as technicians affiliated with a subcontractor, all of whom were Korean nationals, Yonhap news agency reported.

Officials suspect the collapse began as workers poured concrete onto the two-story structure's rooftop, with the ground floors falling to the underground level.

The library under construction was being built by the Gwangju metropolitan government on the site of a former waste incineration plant in the city some 300 kilometres south of Seoul.

Police and labour authorities raided the headquarters of the project's main contractor to seize documents related to the construction to confirm whether the required safety measures were in place.

"We will thoroughly investigate the structural causes of this accident that caused multiple casualties and hold those responsible to account," an official at the Gwangju branch of the Ministry of Employment and Labour said.

Land Minister Kim Yun-duk said Friday that the government plans to introduce a special law to strengthen construction workplace safety and enforce tougher penalties for fatal accidents in response to a growing number of such incidents at construction sites.

Since taking office in June, President Lee Jae Myung has reiterated the need for stronger measures to prevent industrial accidents following a series of accidents at workplaces managed by major construction companies.

/IANS