MOSCOW — A powerful bomb ripped through a bus in central Russia Wednesday morning, killing eight people and wounding at least 53 in what one official called a terror attack.

Investigators were trying to determine whether the explosive device was carried by a passenger or had been planted somewhere on the bus in the city of Togliatti, according to Russian news agencies.

The explosion occurred near a bus stop in the city center as people were going to work. A group of college students had gotten off at the stop just seconds before the blast, and about 20 students were among the wounded, NTV reported.

Windows were blown out of the long green bus, and its roof partially detached from the force of the explosion, which shattered windows of nearby buildings.

Valery Matkovsky, a local emergency official, said that eight people died and at least 53 were injured, mainly from burns and shrapnel wounds. Russian media said that one child was among the dead.

There is a month before crucial parliamentary elections and similar violence has occurred before other votes.

"Due to (the blast's) character, its consequences, the main version being considered is a terrorist attack," Yuri Rozhin, director of the regional division of the Federal Security Service, said in televised comments.

In 1999, just three months before national elections, several residential buildings in Moscow and other Russian towns exploded, killing hundreds. The government blamed militants from Chechnya, where two wars have been fought against separatist rebels.

Opposition activists and Kremlin critics said the government used the blasts to justify sending federal troops back into Chechnya, launching the second war in a decade in the region.

The Volga River city of Togliatti is home to Russia's largest carmaker, AvtoVAZ and has long had a reputation for gang violence as various groups competed for control over the lucrative factory, now state-owned. A factory spokesman could not say whether there were factory workers among the victims.

Vadim Blagodarny, a local 20-year-old photographer, said people walked around in shock in the minutes after the blast, as investigators picked through the carnage.

"If it had gone off just a minute earlier, it would have been much, much worse," he said.

Security at the scene was tight, and some local photographers were either detained or had their equipment confiscated.

The head of the country's main security agency recently warned of the potential for pre-election violence and said police would bolster security and surveillance nationwide before the Dec. 2 vote.