Between March 16, 1997 and April 14, 1997, a high flux level of TeV γ-rays was observed from Mkn 501, using the HEGRA stereoscopic system of four imaging Cherenkov telescopes. The flux level varied during this period from about one half up to six times the flux observed from the Crab Nebula. Changes of the detection rate by a factor of up to 4 within 1 day have been observed. The measured differential energy spectrum of the radiation follows a power law from 1 TeV to 10 TeV. The differential spectral index of 2.47+/-0.07+/-0.25 is close to that of the Crab Nebula of 2.66+/-0.12+/-0.25.