A 20-year-old Christchurch man denies having sex with a 13-year-old girl at a party.

An Invercargill District Court jury trial started yesterday for the man who faces three charges of sexual connection with the girl between April 15 and May 2, 2011.

Crown lawyer Riki Donnelly said the pair had lived in the same neighbourhood and the girl had made it known she had a crush on the man.

On a Saturday night the pair and a couple of other people were drinking at a sleepout at the man's house and later on in the night the man told the 13-year-old he thought she was "pretty hot", Donnelly said.

Later in the night the accused man and the girl had sex, he said.

Defence lawyer David Slater said the defence case was that the sex acts did not occur.