The drama unfolded near the main entrance, but a courageous policeman saved the day by chasing the troublemakers off the site.

The youths, armed with machetes and swords, tried to attack the group on Tuesday evening.

The incident was sparked after a traveller was admitted to the hospital's intensive care unit and a group of travellers came to keep vigil.

Security staff spotted the incident and took action to move innocent bystanders to safety.

Police officers later recovered a number of weapons from the scene, including a machete.

The incident is now being investigated and detectives are examining CCTV footage. They are probing the possibility that it may have been part of a travellers' feud.

A spokesman for Lancashire Teaching Hospitals NHS Foundation Trust said: "The police did attend an incident at Royal Preston Hospital in which a number of youths attempted to attack a group of visitors in the grounds, adjacent to the main entrance at the hospital.

"A police officer who was on site at the time chased off the would-be attackers. The officer's actions undoubtedly prevented the incident escalating."

Sgt Kenneth Flewitt from Preston Police said: "Police were alerted by hospital security staff to a large group of people at the hospital and officers attended as a precaution and to offer re-assurance.

"At this point, officers were alerted to an incident in a car park at the hospital and thanks to the quick-thinking of both hospital security staff and officers, were able to diffuse a potentially very dangerous situation.

"Investigations into the disturbance are ongoing."