A woman was killed and at least 17 other people injured in an explosion on a bus in western Russia, local authorities said early Friday.

Several of the wounded were in serious condition.

“So far there is nothing to indicate that this was a terrorist attack,” Sergei Sokolov deputy governor of Voronezh, where the explosion occurred, told the Interfax news agency.

The bus driver told state-owned Russia-24 news channel that there had been 35 passengers aboard when the tragedy happened overnight Thursday.

“The number of injured has risen to 18… among whom a woman has died,” said Alexander Gusev, Voronezh’s governor.

The explosion went off when the bus was at a stop near a shopping centre. Video taken by passersby and posted on social media showed that the blast tore the roof off the vehicle and blew out its windows.

The national investigation committee said in a statement that it had sent experts from Moscow and opened a negligence case over the upkeep of the bus.