The 19-year-old Wannot Phetchpho was pronounced dead at the district hospital because of multiple trauma to his ribs and lung, a source at the hospital said.

Four of the workers had sustained serious injuries in the accident in Tambon Wian Ka Long, Wian Pa Pao district on Thursday.

Three workers, Siam Klinchod, 23, whose kneecap was damaged, Wanchana Sammon, 36, whose right arm was broken, and Rewat Jaiyen, 33, who broke his leg, were transferred to Chiangrai Prachanukroh Hospital. Another worker, Charoenchai Mainomklang, 22, who had minor injuries, was sent home.

Police are investigating the cause of the collapse of the metal roof.