* Sarenza had sales of more than 250 mln euros
Casino looking to build up online presence
* French sector faces challenge from Amazon (Adds detail, background)
PARIS, Feb 19 (Reuters) - Casino has started exclusive talks over buying online shoe retailer Sarenza, as the French supermarket operator looks to strengthen its online presence in the face of competition from Amazon and other Internet firms.
Sarenza generated sales of more than 250 million euros ($310.30 million) during its last fiscal year, and its planned takeover follows Casino's e-commerce partnership with Ocado , in November, as the French retailer looks to build up the online presence of its Monoprix supermarket business.
Casino, whose credit rating was cut to junk by Standard & Poor's in March 2016, is under pressure to revive profits in France, its biggest market, where it now makes more than 50 percent of its sales, at a time of slower growth in Brazil, its second-biggest market by revenue.
"By acquiring Sarenza and its expertise, Casino Group will consolidate its position as French leader in urban online retail," said Casino Chairman and Chief Executive Jean-Charles Naouri in a statement.
Earlier this month, Amazon announced plans to create 2,000 new jobs in France, in a further sign of the U.S. online giant's ambitions to grow in that country.
In turn, France's traditional supermarket operators such as Casino, sector leader Carrefour and privately-held firm Leclerc have taken steps to deal with the competition posed by Amazon.
Last month, Leclerc announced the launch of a food delivery service in Paris, while Carrefour struck a partnership in China with Tencent and said it would boost its investments in the sector. ($1 = 0.8057 euros) (Reporting by Sudip Kar-Gupta; Editing by Gopakumar Warrier and Louise Heavens)