At least seven people were killed and 40 injured on Wednesday in a powerful explosion on a bus in central Togliatti, a city on Russia's Volga River, rescuers reported.
The cause of the blast has not yet been ascertained but investigators have ruled out a gas explosion because the vehicle did not run on natural gas fuel.
Local officials said 20 people had been hospitalised, two in a critical condition.
He said flying splinters had injured at least another 20 on the road. "Many window panes on the ground and first floors of a nearby building were broken in the impact of the blast," he said.
Togliatti, with a population of about 700,000 people, is home to Russia's largest automaker Avtovaz, which makes cars under the Lada brand.