A "full to the brim" A&E department at the Royal Cornwall Hospital led to 17 ambulances queued outside.
Patients were treated in the ambulances on Monday after a "high influx of elderly and frail patients", an emergency department consultant said.
Olga Zmijewska said there was "no space" for patients after the spike and a ward being closed by fire damage.
She said no patients were harmed despite the "chaos" of the situation.
South Western Ambulance Service confirmed delays handing over patients were "not uncommon", but that crews had experienced extended waiting times on Monday.
Management 'working hard'
Ms Zmijewska said the team was "on top of the game" and assessed patients while still inside ambulances.
She said: "Only patients in need for resuscitation were brought straight in. Hospital management was working hard to create beds.
"Unfortunately with Grenville Ward closed due to fire damage, and high influx of elderly and frail patients we were put in a difficult place."
"In [A&E] we are like willow trees, we can bend to the ground but not [break].
"In all yesterday's chaos we still managed to prevent patients from getting harmed."
The hospital trust urged local residents and holidaymakers to contact their GP or calling NHS 111 if they needed "urgent but not emergency care".
A spokeswoman said: "Health and care services in Cornwall are under pressure despite Covid cases in the County remaining low.
"Families can help, too. If they can take their relative home when they are medically fit, to help them get back on their feet for a few days... we can then free up space in our hospitals for those in real need of emergency hospital care."