A police officer has been injured on the M25 amid climate protests which closed parts of the motorway in Kent, Surrey, Essex and Hertfordshire.
The police motorcyclist was hurt in a collision which also involved two lorries at a rolling roadblock.
The Just Stop Oil group, which is protesting for a third day, said about 10 activists had climbed on overhead gantries "in multiple locations".
The home secretary told police to be firmer against protesters.
Suella Braverman said the "disruption is a threat to our way of life", during a speech on Wednesday.
She told the Police Chiefs Conference: "I urge you all to step up to your public duties in policing protests.
"In recent months and years, we have seen an erosion of confidence in the police to take action against the radicals, the road-blockers, the vandals, the militants and the extremists.
"It is not a human right to vandalise a work of art. It is not a civil liberty to stop ambulances getting to the sick and injured."
Essex Police provided no information on the condition of the officer, who was injured between junctions 26 (Waltham Abbey) and 27 (Theydon).
Chief Constable of Essex Police BJ Harrington said the protests were "putting lives at risk", and warned "someone is going to get hurt".
Surrey Police said five arrests have been made - four on suspicion of intentionally or recklessly causing a public nuisance and one on suspicion of conspiracy of the same offence.
They are all still in custody, police said.
The force said: "This brings the total number of arrests made in Surrey so far to 16.
"Officers are proactively patrolling the rest of the M25, as they have been all week."
Kent Police said protests in Essex were causing disruption at the Dartford crossing for traffic leaving Kent.
A 71-year-old man from Cornwall and a 75-year-old woman from Somerset were arrested by Kent Police.
The disruption comes as the COP27 climate summit is held in Egypt.
Just Stop Oil said in a statement: "This is not a one-day event, expect us every day and anywhere."
It also said the collision of two lorries and the injury to the police officer was "an awful situation".
The group is calling for an end to fossil fuels, renewable energy investment and for better building insulation to avoid energy waste.
One protester, 75-year-old Rachel, posted an online clip from a gantry between junctions eight and nine.
She said: "I'm here because of my five lovely grandchildren. I want to do everything I can to save their future and they are at great risk."
Jade McCormick was travelling to Stansted airport to catch a flight to Scotland to visit relatives she hasn't seen since before the pandemic.
She said: "Traffic was just stopped, at a standstill, and we've had to turn around and I've missed my flight. I'm going to go home and maybe I'll have to drive to Scotland."
Referring to the activists, she said: "I see their point, but in the same breath, when it's causing accidents it's just getting stupid now.
"Police officers have much more serious crimes to deal with but they're now having to monitor the M25 - it's just stupid. I don't agree with it."
At the COP27 summit, Prime Minister Rishi Sunak told world leaders the war in Ukraine was a reason to act faster to tackle climate change.
The Metropolitan Police said 16 protesters had previously been arrested on the motorway in a joint operation with other counties' police forces.
On Sunday, the High Court granted an injunction preventing M25 protests, meaning anyone involved in any such protest could be found in contempt of court.
pursue BBC South East on Facebook, on Twitter, and on Instagram. Send your story ideas to firstname.lastname@example.org.