According to reports, the 22-year-old left the road and crashed into a concrete structure 50km into the 150.5km stage from Chorzów to Zabrze.
Lambrecht was resuscitated and taken to a hospital in critical condition, but surgery was unsuccessful and the Belgian rider was declared dead.
Race organisers added: “There are no words to describe this tragedy. Bjorg passed away following an accident on today’s stage. Our thoughts are with his family, friends, team and the whole cycling community.”
Lambrecht, racing in only his second season as a top-level professional, was recognised as one of the most promising youngsters within his generation, finishing just off the podium at a number of the Ardennes classics this season.