Hospitals treating coronavirus patients could be forced to make life-or-death decisions within days.
Labour MP Dr Rosena Allin-Khan said hospitals are now having to care for critically-ill patients in their thirties and forties.
As a result, she said doctors will have to make "heart-wrenching" decisions soon.
It comes after Boris Johnson revealed the UK does not have enough ventilators to cope during the crisis.
Dr Allin-Khan said medical staff are "frightened" and having to make horrible decisions.
A lack of ventilators
She told BBC Radio 4: "Heart-wrenching and unenviable choices need to be made in the situation that we don't have any ventilators [left]"
"In a matter of days or a couple of weeks we will be having to make life-and-death decisions over who gets the last ventilator," she said.
Dr Allin-Khan added: "In the emergency department we are on the front line. We are seeing a growing number of cases that are growing day by day."
The news comes after the PM warned the NHS could become overwhelmed by the spread of coronavirus in the same way as Italy.
We have patients who have been in their thirties and forties who are now in intensive care and fighting for their lives.
Doctors there are now saving ventilators for patients under 60 because there are not enough of the machines.
Dr Allin-Khan added that previously young, fit and healthy patients are now fighting for their lives.
She revealed: "Some of the sickest patients have been young. We have patients who have been in their thirties and forties who are in intensive care and fighting for their lives."
Yesterday, an 18-year-old boy became the youngest person in the UK to die after contracting the disease.
A 12-year-old girl in America is also fighting for her life on a ventilator after being diagnosed with COVID-19.
Headed for disaster
Dr Allin-Khan added: "We are headed for a disaster if people do not heed the social distancing measures."
At the weekend, many Brits ignored social distancing guidelines. They headed to parks and beaches to enjoy the early spring sunshine.
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