Firemen were pelted with bottles by gangs in Ryelands Park and were forced to retreat to wait for police to act as a deterrent.
One witness said: “The fire brigade got called to a fire in Ryelands Park as they attended local gangs in the park started to throw bricks and anything else they can find.
“The fire brigade were running for their life as several objects came flying at them. That’s when my husband told me to get in and lock the door quickly.”
Firefighters and one fire engine from Lancaster fire station went to the park at 12.17am on Saturday morning after reports of a tree on fire.
They attempted to put the fire out, which involved a small tree trunk, but were forced back to their vehicle by the youths.
A spokesman for Lancashire Fire and Rescue Service said: “999 calls were received to report the fire but fire crews were unable to attend to the fire and had to back off at this point.
“They radioed to the police for advice. The police had someone round who took them to the fire with an escort as a deterrent. The fire was put out.”