Lambrecht crashed around 60 miles from the end of the race from Chorzow to Zabrze in Poland.
He was taken by helicopter to hospital where he later died on Monday.
“The biggest tragedy possible that could happen to the family, friends and team-mates of Bjorg has happened. Rest in peace,” said his team Lotto-Soudal.
Race director Czeslaw Lang said: “It wasn’t a high-speed descent. It was a straight and wide road.
“He had a moment of hesitation, he left the asphalt and the tragedy occurred.
“The injuries were so serious that we called for a helicopter and an ambulance. He was transported to hospital. His heart started beating again but he sadly died during the operation.”
Lambrecht was riding in his second season at the top level of professional cycling and had been regarded as one of Belgium’s most promising riders.
He won the under-23s’ version of the Liege-Bastogne-Liege race in 2017 and finished second in the U23 World Championships last year.
German Pascal Ackermann, who was given the stage victory after the win was taken from Fabio Jakobsen for an irregular sprint heading into the finish line, said “the result of the race doesn’t matter”.
“I was devastated to hear today’s tragic news and I would like to personally send my deepest condolences to the family and friends of Bjorg Lambrecht and everyone at Lotto-Soudal,” he added.
Alejandro Valverde, the 2018 world road race champion, added: “Deeply sorry for the loss of Bjorg Lambrecht, a cyclist who had demonstrated a lot in a few years.
“My deepest condolences to family, friends and team.”