At least two people have been killed and four more injured during shooting at a school in northern Mexico, according to reports.

The shooting occurred in the northern Mexico city of Torreon on Friday morning, in the state of Coahuila, according to the television station Milenio.

A motive for the killings was not immediately clear, nor was the identity of the killer made public.

In video and photos posted on Twitter apparently from the scene, a crowd can be seen forming outside of the school as parents embrace their children. In some images, a black handgun can be seen alongside what appears to be the bodies of two children.

The poster of the video and images said that the posts were obtained as they circulated on social media and in Whatsapp groups.

Local news originally indicated that three people had been killed, but that tally was later lowered.

Torreon, a city with around 679,000 residents, is a round 350 miles southwest from Laredo, Texas, and 200 miles west from the Mexican city of Monterrey.

Mexico has been gripped by spiking rates of homicide in recent years, with the first years of last year seeing more murders during that time than any other year in recent history. During that period, the country's National Public Security System reported that 17,608 people were killed during that time — 5 per cent more than the same period in 2018.

That high death toll has been fuelled in part by cartel violence in northern Mexico, where clashes involving police and gangs have become increasingly commonplace.

The violence has led to international concern, with US president Donald Trump threatening last year to designate the Mexican cartels as terrorist groups, raising concern that he could approve unilateral action against the groups.