Three people were killed after their motorcycle collided head-on with a Bihar Police bus, which dragged it for a couple of metres before its fuel tank burst into flames, police said on Wednesday.

The incident happened near Deoria village on National Highway-531 in Revelganj police station area of Saran district on Tuesday evening, they said.

The impact of the accident was such that the motorcycle got stuck underneath the bus, Superintendent of Police Santosh Kumar said.

"According to eye-witnesses, the bus dragged the motorcycle for a couple of metres, following which the fuel tank of the two-wheeler exploded, causing the fire," he said.

"A case has been registered under relevant sections of the Motor Vehicle Act," he added.

The deceased were identified as Kundan Manjhi (22), Bulbul Manjhi (25) and Kishore Manjhi (24), all residents of Panchbhinda village.

All of them died on the spot, the SP said.

Asked about the purported video of the incident, in which policemen were seen standing at a distance and watching one of the victims burning, Kumar said, "An investigation is underway."

The police personnel were returning from Sitab Diara where they were deployed at the programme to mark the 120th birth anniversary of Jayaprakash Narayan, which was attended by Union Home Minister Amit Shah and UP Chief Minister Yogi Adityanath, officials said.

No policemen were injured in the incident, they said.