Police are trying to disperse around 3,000 people who have gathered for an illegal rave in a forest.
Police are working with the Forestry Commission
Gwent Police are working with the fire service and the Forestry Commission to try to break up the crowds at Wentwood Forest near Caldicot, Monmouthshire.
A force spokeswoman said officers were alerted to the "illegal gathering" at around 2030 BST on Saturday.
Officers were sent out overnight to stop and speak to people at the scene and take details of their vehicles.
Specialist officers and the force helicopter are at the scene.
Gwent police decided it was unsafe to enforce action under the Criminal Justice and Public Order Acts which allows police to force people to move on.
The fire service is also attending a fire on scrubland in the forest which began on Sunday afternoon.