Protocols for entering the NSW Parliament are being reviewed after a person dressed like a "ninja" entered the upper house and threw a paper plane at sitting members.

Police are investigating the incident, which occurred during question time yesterday.

The person, who was dressed in black including a black scarf wrapped around his or her face, passed through security and walked in to the building, and then entered the public gallery of the Legislative Council.

The Herald understands that at no time did the person remove his or her face covering.

The person then shot the paper plane into the air. It is understood to have been a flying petition for Police Minister Mike Gallacher, calling on the government to allow civilians to carry capsicum spray.