Paramedics were attacked by a coach driver as they treated a seriously ill patient in south London, police said.
The London Ambulance Service staff called for urgent help during the “disgusting” incident in Camberwell on Tuesday.
They had been forced to block the road as they treated the elderly patient.
Officers arrested a 51-year-old man after rushing to the scene in Daneville Road at about 9am.
Southwark Police tweeted: “London Ambulance called for urgent assistance to SE5 for their crew being assaulted by a coach driver!
“The crew [was] assaulted whilst treating a seriously ill patient! Located and arrested #Disgusting #Team999."
They added: “The crew are shaken and will now not be able to finish their shift, but no serious injury.
“[They] are assisting us with statements and then they will be finished for the day.”
Witness Gavin Higgins wrote on Twitter: “@RedwingCoaches just watched one of your drivers assault an ambulance driver in Camberwell... police are now on the scene.
“Pretty revolting behaviour towards anyone, let alone someone from the emergency services.”
He later tweeted the LAS, saying: “I just want to say you guys are amazing and I hope you don't have to deal with this s*** too often.
“We've spoken to the police, I hope you're staff are ok.”
Red Wing Coaches refused to comment when approached by the Standard.
It comes after a number of recent reports of abuse directed at paramedics.
Birmingham man Hassan Shabbir apologised on Wednesday after leaving an angry note on an ambulance because it was blocking his drive.
He said he was "disgusted with himself" for leaving the note after finding out his neighbour had died.
A Met Police spokeswoman said: "Police were called by the London Ambulance Service at 9.09am on Tuesday, November 14 to reports that a crew member had been assaulted in Daneville Road.
"Officers attended and arrested a man, aged 51, nearby on suspicion of common assault. He has been taken to a south London police station.
"The LAS crew member did not require medical assistance."
LAS Assistant Director of Operations Darren Farmer added: “It will never be ok to assault our staff who are naturally shaken by this shocking incident.
“On this occasion the ambulance crew were treating a seriously ill elderly patient and transporting her to hospital.
“It is very rare for us to block a road but please be patient if we do. We would only ever stop traffic to deal with a life-threatening emergency and always leave the scene as quickly as possible.”
