The surge in the population of the largely makeshift camp emerged from a head count carried out by authorities on Wednesday.
The new figure of 6,901 people is 2,415 higher than in June.
It is considerably lower however than the figure of more than 9,000 claimed by a charity which works in the Jungle assisting migrants.
The charity included 1,750 people living in more permanent accommodation on the site.
The population of the camp -- which has large numbers of Afghans, Somalis, Sudanese and Kurds, among other asylum seekers -- has fluctuated.
Aid agencies believe the increase is due to an influx of migrants in recent weeks who have arrived from southern Europe.
Migrants gather in Calais, hoping to smuggle themselves aboard lorries that cross the Channel to Britain either through the Eurotunnel or on board ferries.
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