Clubbers were held inside Fabric following an incident at the London club on Sunday morning.
Security would not allow anyone to enter or exit the venue for a sustained period of time after an allegation of rape was made.
A statement was posted to the club's official Facebook page earlier today, reading: "We’d like to apologise to anybody who was unable to leave the venue between the hours of 5am and 6:30am on [Sunday morning].
"Our staff were acting under police advice in response to an alleged incident that happened inside the venue. Fabric takes the safety of its patrons incredibly seriously. We’re unable to comment further as the police are still carrying out their investigation."
A Metropolitan Police spokesperson confirmed that there was an allegation of rape at the club around 4:30am on Sunday.
The security lockdown caused some consternation among clubbers inside Fabric, who were told they could not leave the venue. Those wanting to get into the club were also made to wait outside.
This led to Norwegian DJ and Noir Music/OFF Recordings artist Finnebassen to post a complaint on Facebook which has now been removed.
At around 6am on Sunday he took to Facebook to say: "Basically they won't let anyone leave before the police have done an onsite investigation and taken the info of everyone here. 2500 people or so."
A police investigation is ongoing.