A video of an adorable boy in a tiny police costume interrogating his grandmother has gone viral online.

Four-year-old Christian - whose parents are both cops - melted hearts with his cute attempt to arrest his grandmother Gail while on holiday in Tauranga, New Zealand.

'Open up, it's the police!' Christian can be heard saying in the video, dressed in a custom-made police outfit designed and put together by Gail.

Four-year-old Christian (pictured) in his incredible custom-made AOS police suit designed by his grandmother Gail

'The helmet is a basic black helmet with ear muffs painted and glued on,' Gail told Daily Mail Australia.

'The binoculars have been velcroed on, his overalls came from the UK and I’ve added painted skateboard pads.

'The body protector came from a toy shop and I got him a balaclava and boots to finish it off!'

In the video, Christian says 'I want to handcuff you' to his grandmother while wearing his 'Armed Offenders Squad' (AOS) outfit complete with a helmet and aviators.

The young boy agrees not to arrest anyone after his grandmother tells him no-one had broken the law, and settles for a seat on a stair in his driveway.

Gail revealed she had also made a dog handler outfit, complete with 'puppy section' emblazoned on the suit, for her police-obsessed grandson.

Christian in his 'puppy section' dog handler uniform designed by Gail, with dog, Toby

Gail made the puppy handler suit for Christian (pictured) when he was just one year old

'He actually thinks he is a police officer now!' Gail said.

Christian was so pleased with his new costume that he insisted on wearing it on an outing to the shopping center.

Both Christian's parents are in the New Zealand police force; his mother is a sergeant and in the armed offenders quad, and his father is a dog handler.

With his custom outfits dialed, Christian may be using his interrogation skills just like his parents in years to come.