A passenger bus has swerved off course and driven into a busy pedestrian underpass in Moscow, killing at least four people, Russian news agencies have reported.

Video from the scene posted on social media showed a bus veering off the road and plunging down the steps of a pedestrian underpass on Monday, crushing several people beneath its wheels.

The driver of the bus was detained by police, agencies said, after he lost control of the vehicle. The incident occurred on one of the Russian capital’s busiest roads near the Slavyansky Boulevard metro station.

Monday was an ordinary working day in Russia, where Orthodox Christmas will be celebrated on 7 January.

An unnamed emergency services source told the Tass news agency that the number of fatalities had risen to five people. There were also unconfirmed reports that 15 people had been injured.

The Interfax news agency said investigators were looking into whether the incident had occurred as a result of a technical fault with the bus.

Ten ambulances, fire service personnel, and three medical evacuation helicopters were on the scene, agencies reported.