Dorset police said in a statement to Metro News that they received a report that some type of irritant, possibly CS spray, had been released within the nightclub in the early hours of Saturday morning.
The premises were subsequently evacuated and 40 people were treated by paramedics at the scene. One person was taken to the hospital as a precaution.
Police found no evidence of any substance that posed an ongoing risk to the public during a search of the building. However, the investigation is continuing.
Videos posted on social media show chaotic scenes as hundreds of clubbers attending the freshers event gather outside amid a large emergency presence.
Comment: See also: France: 7 injured after young man refused entry to nightclub rams crowd with car