Two workers were killed and three injured by an ammonia leak today at a Petroliam Nasional Berhad (Petronas) chemical plant, the company said.

"Five contractors were affected. The company however regrets to inform that two fatalities have been reported," Petronas Chemicals Group said in a statement.

The firm is a unit of state energy group Petronas. The leak happened at its Sipitang plant in Sabah around 9.30am.

Petronas Chemicals produces a range of petrochemical products including olefins, polymers and fertilisers.

The company said the leak had been contained and authorities are investigating the cause.

Meanwhile, Sabah Chief Minister Datuk Seri Musa Aman conveyed his condolences to the victims' families.

He said it was regrettable that the incident occurred and added that he was awaiting a report from the national petroleum company on the cause.

"On behalf of the Sabah government, I wish to convey our condolences to the families of the victims," he told reporters after concluding a working visit to Tuaran today.

Sipitang district police chief DSP Awang Arshad Awang Bakar said the fatalities were a local and a foreign citizen.