Recent observations on novel electromagnetic emissions from the microwave to THz range due to tunnel injection of quasiparticles into the c-axis direction of high-Tcsuperconductors are briefly reviewed. The results for YBa2Cu3O7-y, ErBa2Cu3O7-yand Bi2Sr2CaCu2Oy(BSCCO) thin-film tunnel samples and BSCCO single crystals are reported. The observed emission phenomena are qualitatively different between the high-voltage injection regime (V>>/e, where is the gap or gap-sum parameter) and the low-voltage injection regime (V/e). For V>>/e, to which regime most thin-film samples might belong, the nonequilibrium broadband emissions extending to the THz range due to the incoherent plasmon scattering are observable. For V/e, as realized in the case of a BSCCO crystal, in addition to the broadband emissions, a sharp microwave emission peak corresponding to the coherent Josephson plasma peak is observable.