Seven passengers were killed and one was injured when a bus exploded in Myanmar's main city Yangon early Monday morning, a police official said. The blast occurred on Monday as the bus headed north through the city, said the police official. The injured was shifted to hospital for medical treatment. The official said the explosion had been caused by a faulty re-fitting of the bus to run on cheaper natural gas instead of petrol, a common practice in impoverished Myanmar. Meanwhile, security forces cordoned off the area and started rescue work.