A motorist has captured the moment police officers, with weapons drawn, arrested a person following this afternoon's horrific massacres at two Christchurch mosques.

The video, uploaded to Facebook about 3.30pm, showed the two armed officers approaching a stationary car on Brougham St, a major dual carriageway which runs east-west through a residential area in the southern part of the city.

The vehicle, a grey station wagon, had been forced against the kerb of the residential road by a police car. It's front wheels were still spinning, just above the bitumen, as the incident unfolded.

One of the officers was shown reaching into the car, which had its boot and front passenger door open, and dragging a person out as the second officer kept their gun drawn.

As the person, clad in dark clothing, was dragged from the car one of the officers appeared to strike the person with their weapon.

All this occurred as several vehicles continued to drive past. The video is 44 seconds long.

Prime Minister Jacinda Ardern confirmed just after 4pm that police had one person in custody.