Environmental campaigners are blocking some roads across the UK to protest against “inaction” on climate change.
The group, which is calling on the government to declare a climate emergency, said it was beginning a five-day “summer uprising”.
Police warned the protests could cause disruption.
It comes after Extinction Rebellion staged an 11-day protest in April that brought several parts of London to a standstill.
Some of the 1,000 people arrested during that protest appeared in court this week.
On Monday, a blue boat was placed in front of the Royal Courts of Justice in west London, and demonstrators practised yoga and meditated in the middle of the road.
Extinction Rebellion said the protesters were there “to demand the legal system take responsibility in this crisis, and ensure the safety of future generations by making ecocide law”.
“We also stand in solidarity with climate activists around the world who are sacrificing their freedom to fight for climate justice,” it added.
The group is calling on the Metropolitan Police and Crown Prosecution Service to drop all prosecutions against those arrested during the April protests.
Outside Cardiff Castle in Wales, a number of members of Extinction Rebellion parked a green boat in the street, causing severe delays to bus services.
Meanwhile, protesters set up camp on Bristol Bridge with a pink boat bearing the message “tell the truth”, as Avon and Somerset Police and traffic management used concrete blocks to close the road to traffic.
Chief Inspector Mark Runacres, an area commander at Avon and Somerset Police, said the force had cancelled officers’ rest days to make sure it had “sufficient resources” during the protest.
He said road closures could hamper of emergency services to respond to incidents.
“We…are factoring this into our plans so we can continue to keep the public safe,” he said.
He added officers would be “robust” in dealing with any anti-social behaviour and disorder.
Campaigners in Glasgow blocked Trongate at the intersection of Gallowgate and High Street with a 25ft purple boat
Messages saying “act now” and “the future you fear is already here” were printed on the vessel.
Glasgow City Council said Trongate was closed to all eastbound traffic between Albion Street and High Street.
The local authority urged road users to consider taking other routes and said there could be congestion on surrounding streets.
Extinction Rebellion says the UK must act immediately to halt biodiversity loss and reduce greenhouse gas emissions to net zero by 2025.
The government announced in June it would commit to reaching net zero emissions by 2050.