Bursts of the x-ray and electron cyclotron emission are observed in tokamaks during sawteeth and disruption instability. Analysis of the tangential view x-ray emissivity in the T-10 tokamak has indicated that the bursts are connected with the nonthermal electrons (ERA ∼ 15–150 keV) localized around the magnetic islands. Dynamics of the x-ray bursts are compared with the phenomenologically similar bursts of electron cyclotron emission observed in experiments in TCV (Klimanov I et al 2005 Rev. Sci. Instrum.76 093504) and DIII-D (Heidbrink W W et al1999 Nucl. Fusion39 1369). Analysis of the magnetic field evolution during a sawtooth crash has indicated that the nonthermal electrons can be connected with reconnection of the helical magnetic fluxes around the q = 1 surface. Localization of the bursts around X-points of the magnetic islands and growth of the bursts amplitude in plasma with increased reconnection rate indicated that nonthermal electrons can be connected with direct acceleration in strong electric fields induced during a sawtooth crash. The possible effect of the magnetic reconnection on the generation of the powerful runaway beams during major disruptions is discussed.