"A migrant was hit by a freight shuttle at around 2:00am (0000 GMT) on the tunnel site," the official said, adding the victim was probably from Eritrea or Sudan.
At least 10 migrants have died in or near the tunnel since late June.
Around 3,000 migrants, mostly from Africa, Afghanistan and Syria, are camped in the French town of Calais near the Channel Tunnel entrance.
They have made repeated attempts to reach England, often by trying to enter the tunnel or climb onto lorries.
In July, Eurotunnel said 2,000 attempts a night were being made to get into the tunnel, but new fences erected around the tracks, as well as a beefed-up police presence, have greatly reduced the number of intrusions.
Thursday's tragedy comes a week after a refugee was electrocuted the entrance to the Channel Tunnel in France as he tried to climb on to the roof of a train to make his way to England.