Police are investigating a brawl last night between rival rugby league fans during an NRL finals match in southern Sydney.

Supporters traded blows during the Cronulla Sharks versus Sydney Roosters elimination final encounter at Shark Park.

Police and stewards were forced to step in to separate the brawling fans inside the stadium.

NSW Police said in a statement today that investigations have started.

"An investigation is underway after a brawl involving up to 10 people broke out within the grounds of a football stadium in Cronulla last night.

"Police have commenced inquiries into the circumstances surrounding the incident."

Anyone with mobile phone footage or information is urged to call Crime Stoppers on 1800 333 000.

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