France is set to cull about 600,000 poultry birds as the virus spreads among duck flocks in the southwest of the country, the farm ministry said.
France is among European countries - including Britain and Germany - to have reported highly contagious strains of bird flu late last year, leading to mass culls as authorities try to limit transmission from wild birds to farm flocks.
France has already slaughtered about 200,000 poultry and plans to cull a further 400,000 birds, a farm ministry official said.
The culls include flocks where outbreaks occurred, as well as preventive slaughtering of birds in surrounding areas.
As of 1 January, France had confirmed 61 outbreaks of the H5N8 virus, of which 48 were in the southwestern Landes region, the farm ministry said in an earlier website update.
The Landes is part of a duck breeding zone that supplies the foie gras industry.
In other regions, the spread of the virus appeared to be under control, the ministry added.
Meanwhile, German authorities say about 62,000 turkeys and ducks will be slaughtered after bird flu was found on more poultry farms.
Type H5N8 bird flu was confirmed in two farms in the Cloppenburg region in the northern state of Lower Saxony, the Cloppenburg local government authority said.
Cloppenburg is one of Germany's leading poultry production areas.
The H5N8 strain of bird flu is not known to be transmissible to humans.
Risk to humans from the disease is considered low, but past outbreaks among farm birds have needed extensive slaughtering programmes to contain.