An irate motorist spent about 30 minutes sounding his horn at an ambulance that was blocking his way while medics dealt with an emergency.
Paramedics were also “verbally abused” by the man in the altercation in Chesterfield on Tuesday, East Midlands Ambulance Service said.
The service said its security team had begun an investigation and could pass information on to the police.
EMAS tweeted treating a patient “will always come first”.
It added: “Sometimes we will need to block driveways or roads so that we can access a patient experiencing a medical emergency.
“Please be patient with us, one day it could be you or your family member who needs our emergency help.”
The location of the incident has not been disclosed due to patient confidentiality, the ambulance service said.