Oil prices plunged towards a four-year low on Monday after the Organisation of the Petroleum Exporting Countries and its allies shocked the energy market with a huge increase in production, adding to demand woes from the US trade war.

The OPEC+ alliance, led by Saudi Arabia and Russia, agreed at a meeting on Saturday (Sunday AEST) to raise output by 411,000 barrels per day from June, in a move designed to punish overproducing nations including Kazakhstan and Iraq.