Police have arrested at least one person as about 100 Extinction Rebellion activists lay siege to Brisbane's CBD to protest climate change inaction.

Three people had suspended themselves from a large tree over the road on Eagle St, with specialist fire crews called in to remove them.

There was a heavy police presence as officers worked to move protesters off the roads and on to the footpath.

Police have been heard telling protesters to "move on to that side or you will be arrested".

It comes as two Extinction Rebellion protesters remain in custody after locking themselves together on top of a bus on Monday.

They remain behind bars after refusing bail conditions that meant the two men could not attend today's protest.

About 100 Extinction Rebellion activists were causing bus delays up to 15 minutes after they took to Queen St about 5pm, following a gathering in Post Office Square.

Police have seized a number of milk crates that demonstrators were attempting to use as a stage while they interrupted traffic.

Police have also made protesters change their planned march route.

Chanting, "Climate emergency, act with urgency," the protesters were marching through inner-city streets.

Adding to the traffic chaos, a four-vehicle crash stopped traffic on the outbound lanes on the Inner City Bypass.

The Bowen Hills crash has affected traffic on Coronation Drive, the Riverside Expressway and Milton Rd.

The protest came to an end about 6.30pm after demonstrators moved to a park, with traffic in the city clearing.

The Inner City Bypass has cleared since the earlier incident, with no further delays.

Originally published as Traffic chaos: Protesters in trees, four-car crash