A Coronavirus-hit hospital has told people not to go to A&E because of a technical issue with their oxygen equipment.

Watford General Hospital has urged patients not to attend even in an emergency as it declared a critical incident.

The shutdown is related to oxygen levels at the hospital, the Watford Observer reports.

West Hertfordshire NHS Trust has been overwhelmed by COVID-19 cases – with 31 deaths confirmed at its hospitals today.

Anyone requiring emergency care or assistance has been told to visit another A&E for treatment.

It comes as all NHS trusts in England were given an urgent warning to limit the number of people on mechanical ventilators and continuous positive airway pressure machines (CPAP), according to The Guardian.

The letter was sent after a hospital, which has not been named, almost ran out of oxygen last weekend.

NHS England was so alarmed at the horrifyingly low levels of oxygen it wrote to hospital bosses to say the risk was a critical safety concern that would have major consequences.

The letter said urgent action was needed to ensure there was no risk of hospitals running short of oxygen supplies as they come under heavy demand as the outbreak spreads.

Coronavirus can cause life-threatening breathing complications meaning patients have to be put on ventilators to help them breathe. But NHS England said a sudden increase in patients on breathing support could cause a hospital’s oxygen supply to fail completely, cutting off critically ill patients from the help needed to fight the virus.

Hospitals never normally face the risk of oxygen running out, because so few people require ventilation at any one time.

READ MORE: China sends 1,000 ventilators to crisis-hit New York as death toll 3,500.

But the letter from NHS England said – During the coronavirus epidemic, a far greater proportion of patients will require (oxygen) therapy and ventilation, and this presents a clear and significant risk to oxygen delivery systems within hospital estates.

A spokesperson for the West Hertfordshire NHS trust said – As a result of a technical issue with our individual hospital’s oxygen equipment, which does not pose any risk to our patients, West Herts Hospitals NHS Trust declared a critical incident on Saturday, April 4 and has asked that people do not attend Watford General Hospital.

A small number of patients are being transferred to other hospitals in the area, with each patient being fully assessed in line with existing safety guidelines before they are moved.