Paris: Thieves stole two Renoir paintings from a museum in Cagnes-sur-Mer on the French Riviera on Tuesday after breaking in shortly before 6 am through a hole made in a garden fence, the local mayor said.

The thieves had taken two more paintings by the famous Impressionist artist, but dropped them in the gardens as police, alerted by alarms, arrived and pursued them, Mayor Bryan Masson said.

The most valuable works of Pierre-Auguste Renoir have fetched dozens of millions of dollars at auctions.

The two stolen paintings were 'Madame Colonna Romano' and 'Young Woman at the Well', the municipality said. Both belong to Paris' famous Musée d'Orsay and were on loan to Cagnes-sur-Mer's Renoir museum.

French media identified the other two paintings as 'Madame Stephen Pichon' and 'Coco Reading', citing police and local authorities.

Art thieves in Europe are committing more violent robberies and specialist gangs have been replaced by ad hoc opportunists recruited through social media, pan-European police body Europol said last month.

It cited as a prime example a heist at the Louvre Museum in Paris in October last year, when thieves stole €88 million ($102.3 million) worth of jewels, such ​as Empress Eugenie's tiara. Other French museums were also targeted in the past few months.