Cops are under investigation for throwing a party inside a police station for a teenager they arrested on his 18th birthday, seemingly to cheer him up on the special day.

The young man was arrested for stealing a car stereo in the Brazilian municipality of Macau on Saturday, 5th June.

It was only when the officers took him to the police station that they realised it was his 18th birthday, so they decided to buy a cake and a bottle of soft drink to make sure he did not miss out.

Footage of the incident shows the young man sat at a table with uniformed officers standing around him.

He can be seen giving the thumbs up, but otherwise looking glum, as one officer cuts the cake and another opens a large bottle of Coca Cola before they all sing him happy birthday.

The footage shows how the first slice of cake is offered to the victim and the second to his mother, who accompanied her son and the officers to the police station.

The cops can also be heard laughing as one of them snatches the knife used to cut the cake from the suspect.

After the two-minute clip went viral on social media, the local Military Police force (the preventive police force) said it will launch an inquiry into the incident.

The local Civil Police force (the investigative police force) will also launch its own inquiry to ascertain whether any of its own officers were also involved in the incident.