Three Brazilian teenagers reportedly live streamed their own deaths when police opened fire on their car during an anti-drug trafficking raid.

A Facebook Live video said to have been taken on a mobile phone in Rio de Janeiro shows the youngsters laughing and joking as they listen to music in their vehicle.

The music suddenly stops and is replaced by the sound of shouting, and then gunfire.

The mobile phone drops to the floor, causing the image to be obscured, while the sound of shooting continues.

A helicopter can then be heard flying overhead.

The incident is believed to have happened in the São Gonçalo neighbourhood. It left three teenagers dead and a fourth injured, Brazilian news site Folhamax reported on Monday (6 November).

The suspects were alleged to have been security guards for a drug-trafficking gang.

It was not clear why officers opened fire on the youngsters without first attempting an arrest.

The footage has since gone viral online, with some applauding police for their actions.

Rio de Janeiro, Brazil's second largest city, continues to be plagued by crime as drug gangs battle over turf.

Earlier this year, Amnesty International said not enough was being done to tackle the "shocking levels of human rights violations, including soaring police homicide rates".

It noted a disturbing rise in the number of Rio police shooting dead suspects.

Last month, military police and army soldiers conducted several operations in Rocinha, a favela that borders some of Rio's most affluent neighbourhoods in the southern part of the city.

Authorities said they were searching for high-level drug traffickers, who themselves have been battling for control of the area.

On Tuesday their operation expanded to the favela communities of São Gonçalo, with more than 3,500 men from the Brazilian Armed Forces deployed to find criminals and drug stockpiles.

Warning: The footage below contains scenes some viewers may find distressing