KEY POINTS:
A rush-hour fire and explosion on a Shanghai bus killed three people and injured at least 12.
The cause of the incident was under investigation.
Officials would not comment on a report by the official Xinhua News Agency saying the fire followed an explosion.
Xinhua said firefighters estimated about 50 passengers were on the bus at the time.
A report by Liberation Daily and a local witness said some passengers were trapped because the air-conditioned bus had windows that could not be opened.
