A woman and her 10-year-old daughter were killed after being hit by an ambulance in West Bengal's Howrah district on Saturday, triggering violent protests in the area, police said.

The incident happened on the busy National Highway-16, which connects Calcutta to Chennai, bringing traffic to a standstill for at least five hours, they said.

The woman was waiting with her daughter on the roadside for a bus around 6.30 am, when the ambulance hit them. The ambulance, which had no patients, was speeding towards Kolaghat, police said.

The woman and her daughter died on the spot, they said.

Soon, a mob gathered at the spot and blocked the highway, stating that despite several complaints, the administration was not taking any measures to make the highway safer in that area.

As the situation escalated, the ambulance was set on fire and the tyres were burnt, police said.

The protests went on for five hours, leading to kilometres of traffic pile-up on the Chennai-bound flank. The police removed the mob in the afternoon, clearing the road for traffic.

The bodies were also sent for post-mortem.