A 45-year-old man from Zejtun was seriously injured after falling off a ladder while working at the Delimara power station.
The accident took place at around 2.30pm, the police said.
The man fell from a height of around a metre and a half.
He was taken to Mater Dei Hospital by ambulance.
Magistrate Gabriella Vella is leading an inquiry.
The police are also investigating.