Two men face charges after abseiling down the Sydney Convention Centre as part of an environmental protest outside BHP Billiton's annual general meeting.
Police riot squad and rescue officers were called to Darling Harbour on Thursday where about 40 people gathered to protest against the mining giant.
Several groups were involved in the demonstration, including anti-uranium protesters and Aboriginal elders.
Four people abseiled down the building on Thursday to unfurl two banners reading "BHP, Dirty Deeds" and "Australian uranium fuelled Fukushima".
A protest organiser told AAP the first pair of activists were brought down by a police rescue team and taken to Surry Hills police station.
The last two climbed back onto the roof voluntarily and were also taken into custody.
A police spokeswoman on Thursday said charges relating to trespass and risking the safety of others had been laid against two men, aged 38 and 35.
The other two abseilers were expected to be charged later on Thursday.
Arabunna man Kevin Buzzacott was among protesters who gathered for the launch of an alternative annual report, Dirty Deeds, which was distributed to shareholders.
Mr Buzzacott told AAP he would not be satisfied until the company pulled out of northern SA.
"I don't want them up there destroying the country," he said.
"These bastards are killing us out there in the desert."
In Adelaide, a small group of anti-nuclear protesters gathered outside the BHP Billiton office to add their voices to calls for the Olympic Dam mine to be closed.
Friends of the Earth spokeswoman Nectaria Calan said her group was concerned by the company's plans to develop a more cost-effective mining process.
The Wilderness Society offered AGM delegates pamphlets warning the proposed James Price Point development would damage a pristine part of the Kimberley coastline, and calling on the company to drop its plans.