London: A Nazi-looted painting that was hidden for decades has smashed expectations at a rare sale in London as investigators work painstakingly to identify the origins of hundreds of other works from the same haul.

Max Liebermann's "Two Riders on a Beach" was found among more than 1,200 works of art in the Munich apartment of German recluse Cornelius Gurlitt when police raided it in 2012, capturing global attention.

The 1901 oil painting went under the hammer yesterday at Sotheby's for GBP 1.865 million (USD 2.92 million, 2.61 million euros), more than three times the pre-sale upper estimate of GBP 550,000. It is the first from the Gurlitt collection to be auctioned off while the origins of many of the works remain unknown.

"The challenge is to go through the provenance of every single picture in this collection," Sotheby's director Bernhard Brandstaetter said. "It is a lengthy process to establish where a picture comes from, when it was bought and so on," he said, describing the collection as "probably the most significant find in the last 30 years".

Richard Aronowitz, European head of restitution for Sotheby's, described the Liebermann painting as a "scene of great tranquility and joy in nature", adding: "This counterbalances the great sadness and trauma of the work's history."

Wednesday's auction also included a Gustav Klimt portrait lost to Jewish owners during the Nazi regime and had come on sale after the resolution of a dispute between descendants of the artist and the subject.

The painting went for GBP 24,789,000, exceeding the pre-sale estimate of GBP 18 million. Helena Newman, Sotheby's co-head of impressionist and modern Art, described it as "one of his finest portraits to appear at auction in over 20 years."