A gas leak at a key Pakistani nuclear on Tuesday killed two workers, but there was no threat to the public as the situation was immediately brought under control, authorities said.

The leak occurred at the heavy water research reactor complex at Khushab in Punjab province at 2.30 pm (local time), the Pakistan Atomic Energy Commission said in a statement.

The situation was immediately brought under control and two workers lost their lives while controlling the incident, it said.

The leak was controlled by the plant's safety and fire protection division. The plant was undergoing annual maintenance and had been shut down at the time of the incident, the statement said.

"There is no threat to public life as all the (leaked) gas has been burnt in the flare system of the plant," said the statement.

All necessary steps were taken to protect the plant, including the evacuation of personnel as a precautionary measure in accordance with standard operating procedures.

State-run PTV reported there had been a gas leak at the PAEC plant and said employees living in an adjacent colony were shifted to a safer place as a precautionary measure.

The PAEC said orders had been issued for an inquiry to find out the causes of the incident.

The heavy water research reactor in Khushab is a key element in Pakistan's programme for producing plutonium and tritium for nuclear warheads.

The Khushab plant, built with Chinese assistance, is not subject to International Atomic Energy Agency inspections.