The military has been called into drive ambulances after the government refused to meet healthcare workers' demands for a pay rise. The ambulance strike will last up to 24 hours.
British authorities have advised people not play contact sports or get "blind drunk" as ambulance workers go on strike on Wednesday.
Three ambulance unions will stop work for either 12 or 24 hours across England and Wales to protest stagnant wages amid rising inflation.
Workers have promised to respond to life-threatening calls, and around 750 military personnel have been drafted to drive ambulances or help with logistics. But officials warned the system would be under immense strain.
Stephen Powis, national medical director of the National Health Service (NHS) in England, urged people not to drink too much or take uncessary car trips during the strike in order to minimize the number of ambulance calls.
"It's the season of parties, pre-Christmas, so do enjoy yourself but obviously don't get so drunk that you end up with an unnecessary visit [to hospital]," he said.
British Prime Minister Rishi Sunak said the best way to help all workers is to reduce inflation. He claimed giving public sector workers double-digit pay rises would only make inflation worse.
In an opinion piece in the Daily Telegraph newspaper, Health Secretary Steve Barclay accused the ambulance unions of making a "conscious decision" to "inflict harm" on patients.
But Rachel Harrison, national secretary of the GMB union which represents ambulance workers, called these comments "insulting" to ambulance workers. She said workers were "forced" to strike "because year after year the government has failed to listen to them."
"I have never seen such an abdication of leadership as I have from Rishi Sunak and the health secretary," said Sharon Graham, leader of the Unite union, from a picket line in central England.
The ambulance strike comes days after nurses also went on strike for a second time in December calling for a payrise.
The Royal College of Nursing has previously accused Barclay adopting a "macho" negotiating style and said workers would continue to strike in future if the government "keeps giving our nursing staff the cold shoulder."