Climate change activists have attempted to spray a government building with 1,800 litres of fake blood using a disused fire engine.
Extinction Rebellion members used the vehicle - purchased from eBay - to cover the Treasury building in London with dyed-red water in protest at the government "funding climate death".
Protesters say they are highlighting "the inconsistency" between the government pledging to tackle climate change, whilst funding "fossil exploration and carbon-intensive projects".
However, at one stage protesters lost control of the hosepipe, which began spraying protesters and passers-by with liquid.
The Metropolitan Police said they had made four arrests following the protest.
In a statement, they said: "Police were called at 10.17 to Horse Guards Rd #SW1. People on a privately owned fire engine had sprayed a liquid at the Treasury building. No reported injuries. 3 men and 1 woman were arrested on suspicion of criminal damage. Local road closures are in place while police deal."
Among the attendees at the protest was 83-year-old Phil Kingston, who says he is taking action on behalf of his four grandchildren.
An out of commission fire engine was used in the protest
"I come to the Treasury to challenge these practices and to demand radical change in them. In particular the proposal of the Climate Change Committee that UK Export Finance works towards zero emissions by 2050 - it's far too late."
And fellow activist Diana Warner, said: "The situation around global heating and environmental destruction is so urgent that I am risking imprisonment.
"I consider what I am doing now with Extinction Rebellion to be more important than any other work I have done as a doctor and mother.”
The group say 1,800 litres of fake blood were used
The move comes ahead of a major Extinction Rebellion protest planned for October 7, spanning 60 cities worldwide and lasting two weeks.
As part of the so-called 'International Rebellion', activists plan to block 12 areas around Westminster.
It isn't the first time protesters from the group have used fake blood in their demonstrations.
In March, hundreds of Extinction Rebellion activists poured buckets of 'blood' - made from corn starch and beetroot - outside the gates of Downing Street.