Watford General said people requiring accident and emergency treatment should go to the nearest other facility until further notice.
Although the temporary closure was not explicitly linked to Covid-19, The Independent understands that supplies of oxygen are in such demand by those being treated for the novel virus that it is feared they could soon run out.
It is believed the move makes the hospital – run by West Hertfordshire Hospitals NHS Trust – the first in the country to have to offload patients as a result of demand caused by the pandemic.
The issue came to light after a tweet by the trust urged people to not go to the centre’s A&E department.
“Please DO NOT attend Watford General’s emergency department until further notice, even in an emergency,” it said. “Go to your next nearest hospital with an emergency department. Anyone with non-urgent issues should seek advice via https://111.nhs.uk”.
Engineers are currently on site trying to increase oxygen capacity, it is understood.
The closure comes just two days after the same NHS trust announced it was closing a minor injuries department at another hospital in order to deal with coronavirus.
The unit, at St Albans City Hospital, was shut down so staff "could be better directed" to care for patients during the ongoing crisis.