Hundreds of guests at a swingers club in the western German town of Hattingen had to leave in a hurry when the alarm was raised about a possible carbon monoxide leak.

Emergency services were alerted at about 9 p.m. when two guests collapsed — one of whom was initially unresponsive.

When firefighters arrived at the scene, carbon monoxide triggered an alarm they were carrying, and the entire club had to be evacuated.

Firefighters with breathing apparatus arrived to help all of the club's patrons to safety. Crews took 12 guests, who complained of weakness and discomfort, to local hospitals.

"Thanks to the measures, initiated immediately, all of the guests could be rescued from the building," the fire department said in a statement.

According to the local newspaper Stadtspiegel Hattingen, "300 to 350 people or more, mostly lightly clothed, had to leave the swingers club and go to the other side of the street."

Four of the guests complained to the newspaper that they were left in the cold for more than an hour and that passing busses were not flagged down to pick them up.

Party did not resume

The club patrons were eventually taken to a makeshift assembly area to receive medical checkups. Several people who complained that they felt ill were taken to hospital.

A subsequent check of the building showed the carbon monoxide had dissipated. Later in the evening, guests were allowed back to retrieve their belongings.

"The guests were allowed back into the building again to pick up their things, but the party did not continue," a fire department spokesperson said.

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The club is billed as a venue for "open-minded and outgoing people" to enjoy atmospheric evenings alone, as couples, or groups.

Some 160 emergency workers were involved in the operation, with crews called in from the nearby city of Bochum and other towns.

Police and specialists have launched a preliminary investigation into the cause, with a decision to be made on Monday about any further steps​.​

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