We report the detection of rapid wavelength and intensity variations of narrow components in absorption line profiles of the hot galactic supergiant P Cygni. During most of the time, in 1 week of observations, there were two such components present. Although the period of observation is too short for firm conclusions, the velocity curves do not contradict the photometric period of 17.3 days. These curves may be interpreted as a double wave, `swinging in counterphase'. This observation would suggest the presence of one long wave over the stellar surface. The waves are possibly gravity waves with wavelengths of the order of half the stellar radius.