The peloton approached the level crossing and was cut in half as the barriers descended.
Some riders were clipped by the barrier as it fell, while others squirmed to the side and raced over the crossing.
As security personnel ordered those behind to halt, a few daredevils broke free, including one reckless rider who made it off the track just eight seconds before a TGV high-speed train thundered past.
The company responsible for France's state trains, SNCF, wants police action against cyclists after the scary scenes, lambasting those competitors who darted across.
The company wants "several riders" to be punished for breaching "all safety rules".
"Millions of television viewers saw live this extremely serious and irresponsible action which could have been tragic," said SNCF.
"A few seconds later, a TGV ran on this line and could have hit the peloton."
However, the cyclists in question have been defended by the organisers of the race.
"It wasn't possible for the leading riders to stop sufficiently safely," said Guy Dobbelaere, president of the jury of race commissioners.
"The peloton was 10 metres away when the barrier started to close."