MEXICO CITY, Nov 7 (Reuters) - Five people were killed in a prison riot in the northwestern Mexican port city of Mazatlan on Friday, Mexican media said, the third deadly clash inside the country's overcrowded prisons in two months.

Police departments in Mazatlan declined to comment and Sinaloa state officials were not immediately available.

A shootout erupted in the prison early in the morning when inmates from different gangs clashed, Reforma newspaper said.

El Universal daily said five people were killed and a number of others were injured in the prison, home to some 1,100 inmates.

Guns and illegal drugs are a staple in most Mexican prisons, which suffer from overcrowding and corruption and are full of drug cartel and organized crime convicts.

Some 19 inmates were killed in a prison riot in the violent northern border city of Tijuana in September, including two U.S. citizens, and at at least 21 were killed in a gunbattle in a prison in Tamaulipas near the U.S. border in October.

President Felipe Calderon's army-led clampdown on Mexico's powerful drug smuggling gangs has sparked a wave of cartel violence that has killed more than 4,000 people this year and also put many cartel members behind bars. (Reporting by Cyntia Barrera Diaz; editing by Mohammad Zargham)

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