The firing took place Friday night when the bus from English Bazaar was on its way to Nalagola.
"We have detained seven people for questioning," Malda Superintendent of Police Kalyan Mukherjee said.
The firing followed a bomb explosion in Jalpaiguri district which has so far claimed six lives besides injuring three.
While police suspect the Kamtapur Liberation Organisation behind both the incidents, the separatist outfit has denied its involvement in Thursday's bomb explosion.
--IANS (Posted on 28-12-2013)