Saturday's jailbreak is the country's biggest since Mexico began a war on drug cartels four years ago [EPA] 

At least 140 inmates have escaped from a state prison in the northern Mexican city of Nuevo Laredo, near the border with the US state of Texas.

Police said the prisoners easily but slowly filed out of the jail's main entrance with the complicity of prison guards on Saturday.

"From preliminary investigations, we know that the inmates left by the service vehicle area and were allegedly helped by the penitentiary centre staff," Antonio Garza, a local security chief, said.

"The staff of this prison is at the General Attorney's office disposal and and they have betrayed the state government."

Placing the blame

Mexico's interior ministry has blamed the escape on local authorities, saying they did not properly guard the facility.

The head of the state's jail system has been suspended following the incident.

It is the country's biggest jailbreak since the government began its war on drugs four years ago.

It is not clear who orchestrated the escape, but police sources say a Gulf of Mexico cartel may have offered to free gang allies on condition that they switch sides.

In July, authorities found out that prison officials in a northwestern state had allowed convicts to escape for the night to carry out revenge attacks.

Source: Agencies