Auction house Christie's reported record-breaking sales of post-war and contemporary art for January-June, helping push total sales to 2.69 billion pounds ($4.6 billion) including a Picasso painting and 51 other works fetching $10 million or more.

Sales rose 12 percent during the first half, compared with the first half of 2013. Among the major sales were Monet's "Nymphea", which sold in New York for $27 million in May, and at the same auction Picasso's "Portrait de femme (Dora Maar)", which went for $22.6 million, including commissions.

In London, Francis Bacon's "Portrait of George Dyer Talking" sold for 42.2 million pounds in February, and an egg by U.S. artist Jeff Koons sold for 14.1 million pounds.

Christie's said on Wednesday that 24 percent of all buyers in the first half were new to the house.

It also reported a 70 percent increase in online activity.

"Digital engagement and new buyers coming to the market have continued to drive growth; new clients represented 24 percent of all buyers and 15 percent of the sales total in the first half of 2014," Christie's said.

The auction house said it was opening a new Shanghai office in October and new galleries in New York City's Rockefeller Center in November to keep pace with growing demand.

"Our strategy to engage this growing audience for art through auction, private sales and digitally has been validated and again welcomed many new buyers," Steven Murphy, its chief executive officer, said in the statement. ($1 = 0.5834 British Pounds)