A COUNCIL-contracted Esplanade security guard has been fired after allegedly blackmailing a teenage girl into performing a sex act on him in a toilet.

The girl, believed to be in her late teens, was caught supplying alcohol to underage youths on The Esplanade by the guard.

He then allegedly told her to perform the sex act on him, or he would call the police.

But at least one teenager managed to catch the act on their mobile phone's video camera and told the security firm.

A council source contacted The Cairns Post this week about the incident, saying staff were disgusted by the incident.

The source was angry the incident had not been reported to police.

Police last night confirmed they were unaware of it.

The guard, working for ISS Security, a firm sub-contracted to Cairns City Council for Esplanade security, was fired after the council was told of the incident in late December.

ISS Security is the same firm at the centre of recent claims of poor security performance at Cairns and Brisbane airports.

One youth spoken to by The Cairns Post on the Esplanade said she had heard boys from her school boasting that footage of the act was circulating around schools via mobile phones.

Cairns City Council yesterday moved to distance itself from the alleged incident.

"Security is provided by a contractor. It's a security firm," a spokeswoman said.

"Council does not have a role in selecting their staff or disciplining their staff.

"When council was advised of the alleged incident, it advised the security firm that such actions by its staff would not be tolerated and has since been informed that the person allegedly involved has been dismissed."

The security firm would not speak to The Cairns Post.