A witness said they were waiting in the A&E unit when the woman came in with a ‘broken container’ and was immediately rushed outside by staff.
Police have since confirmed the department had been closed as a precaution after a patient attended had come into contact with an irritant substance.
CJ Churchall-McKenzie earlier told Mirror Online:”I’m in the waiting area. We are not being allowed to leave or move departments.
“The police have locked the unit down (as) someone came in with something she had broken open and they sent that person straight outside. They then locked the hospital down.
“They have just sent a doctor out to get a swab to find out what the woman’s been exposed to.”
Cj later said: “I overheard a staff member saying it may have been a type of battery acid.”
Mazlum wrote on Twitter: “Barnet hospital on lockdown after chemical indicdent. Everyone being checked up by doctors. no one is allowed in/out.
“One patient is said to have something to do with the chemical. no information given by the police. They are checking if anyone has left the hospital.”
A Met Police spokesman “Police were made aware at around 1.45pm on Friday, March 30, that the Accident and Emergency unit at Barnet Hospital had been closed as a precaution after a patient attended having come into contact with an irritant substance.
“The patient is believed to have come into contact with the substance elsewhere. Not on hospital grounds.
“Police and London Fire Brigade are on scene.”
MPS Barnet wrote on Twitter earlier: “Barnet General Hospital A&E is currently closed for an ongoing incident. Police are on scene and dealing.”
A spokeswoman for the Royal Free Hospital Trust, which is in charge of Barnet Hospital, has now told Mirror Online that the A&E unit has reopened.
She confirmed an incident did take place earlier but could not comment further at this time.
The incident comes at the same time that a nearby service station in Hertfordshire was closed for “a few hours” after a chemical spillage.
It’s not clear whether the spill at The Welcome Break service station on the M25 at South Mimms was at all connected to the chemical incident at Barnet Hospital.
Herts Police said in a tweet earlier: “The Welcome Break service station, at #SouthMimms, has been closed following a chemical spillage.
“The area has been sealed off whilst the situation is being assessed and to protect the public.
“The service station will be closed for a few hours whilst the area is cleaned.”