Police say a police officer who elbowed an oil protester five times while he had his arms pinned by other police was "reacting proportionately to prevent being further assaulted".

Four people were arrested during an attempted blockade of the Petroleum New Zealand conference in Wellington on Tuesday.

Protesters tied themselves to the TSB Arena building and there was a strong police presence.

Newshub coverage of the protest clearly shows a female officer striking a protester at least five times with her elbow. The protester at the time has both arms restrained by other officers.

The item does not show what led up to the officer striking the protester, who appeared to be one of those arrested, but Inspector Brett Amas says the footage shows the officer was attacked.

"We are satisfied that it shows one of our staff being assaulted, with two protesters aggressively gripping and pulling the hair of a female officer," he said in a statement.

"The officer reacted proportionately to prevent being further assaulted.

"While the video clearly shows confrontation, based on the information we have, it cannot be assumed or concluded that excessive force was used by police."

Amas said anyone wishing to complain about policing of the event could do so through police or the Independent Police Conduct Authority.

- NZ Newswire