The former attorney-general of Papua New Guinea has called for Australians to help investigate the police shooting at student protesters that left as many as a dozen wounded.

Kerenga Kua told Fairfax Media from Port Moresby that police armed with automatic weapons had fired directly at the students on Wednesday after they attempted to march to the Parliament.

Mr Kua said the police response was "complete overkill and completely unjustified". A hospital in Port Moresby said three students remained in intensive care with gunshot wounds.