Extinction Rebellion protesters have now moved to Park Street and College Green.
Motorists can be seen waiting behind them - including a bus.
We are reporting live updates on the Extinction Rebellion protest action here.
Bristol City Council has issued the following update on Twitter: "Road blocks update: Protestors are temporarily blocking a number of roads in the city centre particularly around College Green so please plan your travel carefully and allow extra time for your journey."
Where else are they?
A large pink boat has been positioned on Bristol’s oldest bridge, at the southern end of Castle Park, and one of the main routes into the city centre has been closed down completely.
The campaigners said the protest will last all week - and is part of a co-ordinated operation with protests in several other cities in the UK.
Avon and Somerset police have been working with Extinction Rebellion organisers in an effort to balance people's rights to protest alongside the desire to keep disruption to a minimum, they say.
In liaising with the group, police chiefs have made plans based on where the protesters have indicated their activities will take place, mainly around the Bristol Bridge area.
Area Commander Chief Inspector Mark Runacres said: “We’re proactively engaging with the protesters, local businesses and the wider community to ensure people are being kept informed of any developments that may impact on their daily lives.
“Due to the potential scale of the protest and the impact it may have, we’ve had to cancel officers’ rest days to make sure we have sufficient resources in place over the five days."
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