We study transitions of hadronic matter to three-flavour quark matter (3QM) locally both for shock-induced and diffusion-induced conversions. The former is the transition via two-flavour quark matter triggered by a rapid density rise in a shock wave and the latter is induced by diffusions of a seed 3QM. Not only the jump condition on both sides of the conversion front but the structures inside the front are also considered by taking into account what happens during the conversion processes on the time scale of weak interactions. We demonstrated that the combustion will occur in the so-called endothermic regime which has been ignored in the discussion so far. We also find that the deflagration front is unstable in the exothermic regime but stable in the endothermic regime, which is quite contrary to the ordinary combustion. It is also confirmed that strong detonation and weak deflagration are always obtained for shock-induced and diffusion-induced combustion, respectively, regardless of whether in exothermic or endothermic regime.