Assaults and drugs at WA concert

More than 20 people have been charged with drug and other offences during the Groovin the Moo concert in Western Australia's South West region.

Police said most of the 20,000 patrons at Hay Park in Bunbury on Saturday were well behaved, but 22 were charged - half of them with possessing drugs.

A police officer and a security guard were assaulted, but neither of them was seriously injured.

A Perth man, 34, was also knocked unconscious and suffered a swollen lip, bruises and swelling to his temple and jaw.

A man is assisting police with their inquiries.