MEXICO CITY (AFP) - Gunfights erupted in broad daylight on Friday in a Mexican city close to the US border plagued by drug cartel violence and several vehicles, including a school bus, were set on fire.

There were no immediate reports of casualties from the clashes in Reynosa, a city of 610,000 located across from the Texas town of McAllen.

Authorities suspect the gun battles, which began in the early afternoon, are related to a power struggle within the Gulf cartel, an official in the Tamaulipas state prosecutors office told AFP.

"We don't know if there are victims because we can't reach the locations (of shootings) for the moment," the official said.

Gunmen blocked streets with vehicles, setting several on fire, including a school bus, the official said. The tactic is used to prevent rival factions or government forces reaching the area.

The local daily El Manana reported that US authorities closed two border crossings.

Reynosa residents posted pictures on Twitter of burning vehicles and people lying on the ground in panic.

The government has dealt blows to the Gulf cartel in recent years with the arrest of several leaders. Authorities have blamed a surge of violence in Tamaulipas this year on the gang's infighting.

The gang has also battled its former allies, the Zetas cartel, for control of drug trafficking in Tamaulipas.