The Turnbull government has abruptly reversed its opposition to an international investigation into atrocities against Rohingya Muslims, including mass rapes, torture and the slaughter of babies.

The government has co-sponsored a resolution at the United Nation's top human rights body in Geneva to send a fact-finding mission to Myanmar to investigate what the UN says could amount to ethnic cleansing and crimes against humanity.

Human rights groups praised the 47-member forum for passing the resolution in Geneva on Friday without a vote and despite Myanmar saying it was "not acceptable."

Australia's late turn-around came after human rights groups condemned Canberra for calling on Myanmar to conduct its own investigation with international help into the atrocities in the country's Rakhine state, home to more than one million Rohingya.