AN officer who struck two suspects with a baton during a city arrest now faces an official investigation.

South Australia's Police Complaints Authority will look at the actions of the officer and his partner after Seven News recorded the incident and aired the footage.

The men were sitting on the ground in Whitmore Square in central Adelaide when one officer struck them during their arrests at Whitmore Square about 2.30pm.

Witnesses said both men were pepper-sprayed before an officer struck one man twice with his baton and hit the other man three times.

A police spokesman said the officers were questioning the two men about alleged drug dealing.

Police have confirmed the Police Complaints Authority will investigate.

The arrested men have been charged with hindering and resisting police and one was also charged with assaulting a police officer and possessing drug paraphernalia