BHP Billiton said on Monday it is declaring force majeure at its coal mines in Australia's Bowen Basin due to prolonged union strikes and heavy rains.

Some mines in Australia's eastern Queensland state, where the mines are located, are still recovering from heavy flooding in 2011 and about 3,500 unionised workers have been staging rolling work stoppages at the mines since mid-2011.

(Reporting by Rebekah Kebede)