Police had to cut free an environmentalist who chained herself to a door during an anti-nuclear protest in one of several demonstrations in central Brisbane.

The woman stood firm while another student refused to hand officers the key to the bicycle lock wrapped around the entrance to engineering company Parsons Brinckerhoff in Edward Street.

The firm is assessing sites for a proposed nuclear waste dump in the Northern Territory.

Both women were charged with failing to obey a police directive and taken to the police watchhouse in Roma Street, where a man in the group climbed a tree and fell onto an awning.

He was charged with disorderly conduct.

All were bailed to appear in the Brisbane Magistrates Court later this month.

Earlier, about 200 students gathered in front of Queensland Premier Peter Beattie's empty office to demonstrate against two controversial dams, north and south of Brisbane.

Mr Beattie was in Canberra for the Council of Australian Governments (COAG) meeting.

The protesters constructed a mock dam wall and makeshift rivers from sheets of blue material outside the Executive Building in George Street before moving to Elizabeth Street to protest against construction of Brisbane's north-south tunnel, due to start next month.

Some of the students then moved onto the inner suburb of Milton to demonstrate at the offices of mining company Rio Tinto against the deaths of 150 Papuan miners.

Inspector Stephen Carmody of Brisbane Central District Police said most of the protesters were well behaved.

"The feedback we were getting from the general public was of general interest and amusement," Insp Carmody said.