We report the observation of multiparticle coherent emission in the very far infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current exceeds a threshold value, suggesting an instability-driven modulation of the electron bunch density. For the operating conditions reported, the spectral content of the coherent emission is peaked near a wavelength of 7 mm. This wavelength is much shorter than the nominal electron bunch length, indicating the presence of a density modulation within the bunch.