TITLE: GCN CIRCULAR NUMBER: 29745 SUBJECT: GRB 210402A: NOT optical upper limits DATE: 21/04/03 02:55:03 GMT FROM: Dong Xu at NAOC/CAS Z.P. Zhu (NAOC, HUST), D. Xu (NAOC), L. Izzo (DARK/NBI), J. Martikainen (NOT) report on behalf of a larger collaboration: We observed the field of GRB 210402A (Page et al., GCN 29743) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 00:19:22 UT on 2021-04-03, i.e., 2.23 hr after the burst, and we obtained 3x300 s and 5x200 s frames in the SDSS r- and z- filters, respectively. Preliminary analysis reveals that no optical transient is detected in our stacked images within or at the edge of the current XRT error circle (3.5 arcsec; Page et al., GCN 29743), down to limiting magnitudes of r ~ 24.6 and z ~ 23.2, calibrated with nearby PanSTARRS stars. Compared with the bright X-ray afterglow and no much X-ray column density excess, it may indicate that the burst is a high-redshift one. NIR follow-ups are strongly encouraged.