The Warehouse car park at Timaru where the couple was caught in the act.

Most people wouldn't consider The Warehouse to be a particularly romantic place, but for one Timaru couple the allure of the big red shed was all too much.

A 47-year-old man and 40-year-old woman were arrested on Monday night after police received reports of a sexual act being committed in a parked car at The Warehouse.

Sergeant Grant Lord said the pair were arrested for offensive behaviour, and were issued with pre-charge warnings.

Their romantic rendezvous was interrupted when a member of the public spotted the pair.

The onlooker later blasted the "disgusting pigs conducting the lewd act" online.

"I hope havn [sic] a police spotlight and a lady cop knocking on ya windows gav ya a good fright," they posted.