A long period of hot weather threatens to hit the wine harvest in France's famous Burgundy and Beaujolais regions, experts told AFP on Tuesday.

Production could be down, although quality will remain high, they said.

Output could fall by as much as a third in Beaujolais, said Florence Hertaut, wine expert at the agricultural chamber of commerce in the Rhone region.

"The dryness has meant that the grapes, the fruit, are especially small," she told AFP.

Christine Monany, from an association representing wine-growers in Burgundy, said a "small decline in quantity can be expected due to the heat."

"When the vine lacks water, this limits how long it can grow," she said.

Much-needed weekend rain "allowed the vines to get going again but the grapes are still small. They will grow a little bit but they will not reach a normal size," said Monany.

While the heatwave is expected to have an impact on the quantity produced, the quality is still expected to be high.

Hertaut said the heat has produced "very healthy" vines, as it has dried up any hint of dampness, which can lead to fungus diseases impacting the grapes.

In Burgundy, "we can even expect an excellent crop" even if "it is the last few weeks which will be decisive."

France has just sweltered through its third-hottest July since 1900 with less than half the amount of rain than usual, according to French meteorologists.

"In terms of the dryness on the ground, the situation remains tense over a large part of the country," said Francois Vinit from Meteo France, the national weather forecaster.

This has also had an impact on other French food production. Cabbage and corn crops could be down as much as 50 percent, according to local producers.