Three electrical workers – Direk Intarangsee (37), Warawut U-Nath (23) and Thosapol Faksawat (26) – were electrocuted and lost consciousness while installing an electrical system inside the sewer at the condominium near Wat Bang Na Nai.
Condo security guard Sarima Wakachi (37) was also electrocuted and lost consciousness when he went into the sewer to help the three workers.
Police officers, medical staff and rescuers took more than 20 minutes to bring all victims back up to the surface before sending them for medical treatment.
However, Pol Lt-Colonel Yuthasin Karin, deputy superintendent of Bang Na Police Station, said Thosapol and Warawut died.
He added that the Department of Health and police officers will survey the scene and summon related parties for an investigation.