The incident occurred when Sarkar was returning from his party office at Rajgang last night when the biker hit him from behind, leaving him seriously injured, a police officer said.
He was admitted to the North Bengal Medical College and Hospital where he died this morning, they said.
Efforts were on to track the motorcyclist, he said.
Locals blocked road in Rajganj area this morning for over two hours demanding proper traffic arrangements. The blockade was lifted at the persuasion of the BDO N P Sherpa, he said.