Taiwanese prosecutors have sought an arrest warrant for a construction site manager whose truck is believed to have caused a train accident that killed at least 50 people, as authorities warned on Saturday more bodies could be found in the wreckage.

Friday’s crash, Taiwan’s worst rail accident in seven decades, occurred after an express train hit a truck that had slid down a bank next to the track from a construction site. The manager of the construction site is suspected of having failed to engage the brake properly.

The train was carrying almost 500 people on its way from Taiwan’s capital, Taipei, to Taitung on the east coast, when it derailed in a tunnel just north of Hualien.

Ministry of Justice Department of Prosecutorial Affairs Director-General Lin Jinn-tsun told reporters on Saturday that prosecutors had applied to the court to arrest the manager on charges of causing death by negligence and forged documents.

“Prosecutors will certainly step up investigation and understanding of the crimes or of other suspects involved in the case,” Lin said.

He told Reuters he expected the court to approve the arrest on Saturday.

Yu Hsiu-duan, head of the Hualien prosecutors office, said prosecutors were at the scene collecting evidence.

Workers on Saturday began moving the back part of the train, which was relatively undamaged having come to a stop outside the tunnel, down the track and away from the site of a accident.

The more heavily damaged sections of the train remained mangled inside the tunnel, where fire department official Wu Liang-yun said there were likely more bodies.

“We’re still carrying out rescue work,” he said.

Forty people remain in hospital, among the 178 reported injured.

President Tsai Ing-wen visited hospitals in Hualien to speak to family members and survivors, expressing thanks to ordinary people and non-governmental groups who had stepped forward to help.

“This shows the good side of Taiwanese society,” she said at a military hospital.

The government has declared flags should be flown at half mast for three days in a show of mourning.

The accident happened at the start of a long holiday weekend. The train was packed with tourists and residents going home for the traditional Tomb Sweeping Day, when people clean the graves of their ancestors.

Taiwan has no domestic travel restrictions as the island has the Covid-19 pandemic well under control, with only a handful of active cases in hospital.

Before the Hualien accident, Taiwan’s worst train crash occurred in 1948, when 64 people are estimated to have died when a train caught fire.