The gang vandalized the bus, Na 5 Kha 7111, of Arughat Transport at Phinam while it was heading for Gorkha Bazaar, the district headquarters, from Arughat.
The injured are Buddha Laxmi Shrestha, Mina Gurung and driver Ram Bahadur Roka. Identification of a woman is yet to be ascertained.
Police said the mob also vandalized four motorcycles.
Of late, the association has resorted to vandalism after its syndicate was broken by other entrepreneurs. Chairman of Gorkha Transport Entrepreneurs Association, Ram Hari KC has taken responsibility for the attack.
Passengers have been left stranded after transportation along the Arughat-Gorkha Bazaar came to a complete halt following the attack.
In Pictures: Tense Balkhu