The incident happened near DS College in the Town area when a speeding truck hit a motorcycle driven by a youth from the back, Katihar SDPO Rakesh Kumar said.
"The youth had a narrow escape but his mother, Sunita Devi, who was riding the pillion came under the wheels of the truck," Kumar said.
Angry over the accident, locals blocked the road, torched the truck and looted fertlizer sacks laden on it, he said, adding that few policemen were also injured in the brick-batting.
In Araria district, two persons were killed and six injured in a truck-autorickshaw head-on collision near Lahtora village on NH-57 under Town Police station area, police said.
Among the eight passengers of the autorickshaw, two identified as Saidur Rahman (65) and Md Mansoor Alam died on the spot while six others have been admitted to the Sadar hospital with injuries, police added.