Three construction workers suffered severe burn injuries Monday and fell from the third floor of a house being built in the central region province of Ninh Thuan.
It is believed that the accident was caused by an electric shock.
Eyewitnesses said the workers were carrying an iron bar up a house and one head of the bar hit a middle-voltage power cable in front of the house. There were sparks and a big blast when it happened, they said.
Immediately after the blast, the workers - Nguyen Xuan Tan, 17, Nguyen Thanh Tuan, 28 and Nguyen Quoc Tuan, 26 - fell from the third floor.
Nguyen Thanh Tuan is said to be in a critical condition while the other two have been declared out of danger by doctors.
Le Thi Thanh Y, a resident opposite the house, said: "I saw an iron bar going through the net covering the construction and hanging on the power cable."
The house being built stands just 50 centimeters away from the middle-voltage power pole.
Police are investigating the accident.