Provincial police confirmed the crash took place in Michoacan state. The pilot died and five people, including Mireles, were injured, the Latin Times reported.
Mireles was airlifted to Mexico City where he remains under tight security in critical condition.
Mireles became a strong force battling the drug cartels increasingly taking over towns in Michoacan, leading violent attacks. The cartels have fought back, burning buses, blocking roads and forcing the state-run bus company to stop running for a time.
Officials did not say what specifically caused the crash but initial investigations suggest it may have happened as a result of a mechanical failure.
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