"The explosion was on a very busy street. There are five confirmed fatalities," Balquin told local Catholic radio station DXMS.

The late-afternoon blast damaged at least four vehicles and triggered a fire that engulfed a nearby mortuary and a tyre repair shop, he added.

No group has claimed responsibility for the attack, and Balquin said the motive was still being investigated.

Cotabato is a mixed Muslim-Catholic city on the main southern island of Mindanao, where Muslim insurgents have waged a decades old rebellion that has claimed 150,000 lives.

It was the second bombing to hit Mindanao in 10 days.

A powerful blast at a restaurant packed with doctors and pharmaceutical salesmen left eight people dead on the Mindanao city of Cagayan de Oro on July 26.