At least two guards have been killed and nine prisoners have escaped during a jailbreak in southern Mexico, officials say.

A prison warden and a prisoner were also injured when a group of men stormed the prison and opened fire.

The attack happened in the early hours of Sunday in the town of La Union, in the south-western state of Guerrero.

Correspondents say jailbreaks are common in Mexico’s overcrowded prisons, which house inmates from rival gangs.

Guerrero’s Public Security Secretariat said a “group of men armed with rifles and guns” stormed the building at 05:00 local time (10:00 GMT), killing the guards and freeing the inmates.

In a statement, it said that federal and state police were using helicopters to find the escaped prisoners.

It added that the whereabouts of the prison’s director, Manuel Chavarria, was unknown; local media say he fled the attack.

Guerrero is one of the states most affected by fighting between organised criminal groups and by a military offensive against drug cartels that has left an estimated 70,000 people dead nationwide in the past six years.