A mob of around 40 stopped the buses in morning hours and set them ablaze after asking passengers to get down, they said.
Nobody was injured in the incident.
Though an FIR has been filed against unidentified persons, police believe that the rioters were the supporters of Hardik and vented their anger after learning about his hunger protest.
"It seems that the news about Hardik's hunger strike in Lajpore jail here has sparked off the protest. Around 40 rioters stopped two state transport buses and set them ablaze early today morning. No one was hurt in the incident. A case of rioting has been lodged against a mob of 40," said Sarthana in-charge police inspector V A Patel.
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Hardik launched the fast at the jail, where he has been lodged since September in two sedition cases, demanding reservation to his community in government jobs and education under OBC category and immediate release of Patel quota leaders, including him.
Meanwhile, state Transport Minister and newly-elected state BJP president Vijay Rupani urged the protesters to keep calm.
"Agitators surely have the right to protest. But such violence will only harm them instead of benefiting them. No one should take law in their own hands. Earlier also, many buses were torched (during quota stir last year). I urge them not to indulge in such activities," said Rupani.