Christie’s sales of art and collectibles rose to a record 2.9 billion pounds ($4.5 billion) in the first six months of the year as demand from new clients increased.

The tally at London-based Christie’s, the world’s largest art broker, increased 7.4 percent from the same period in 2014 as collectors favored Impressionist, modern, postwar and contemporary works, the company said Monday in a statement. In May, Christie’s sold the most expensive artwork at auction, Pablo Picasso’s 1955 “Les Femmes d’Alger, (Version ‘‘O’’),” for $179.4 million.

A growing number of wealthy collectors is entering the market, focusing particularly on contemporary works they consider good investments. New clients increased to 24 percent of all buyers in the first half, and in the middle market, defined as lots priced 100,000 pounds to 1 million pounds, they rose 14 percent, Christie’s said.

“It’s the biggest sales we’ve ever had and it’s across all parts of the business,” Stephen Brooks, global chief operating officer of Christie’s, said in an interview.

A record $2.7 billion of art was sold at Christie’s, Sotheby’s and Phillips in day and evening sales in May in New York. During these auctions, Christie’s held an additional event, “Looking Forward to the Past,” that united modern and contemporary works spanning the 20th century. That sale helped Christie’s total $1.7 billion in purchases in one week.

Christie’s also sold Alberto Giacometti’s “Pointing Man” sculpture for $141.3 million in May, an auction record for any work in that medium.

Postwar, Contemporary

“Our clients are eclectic and are interested in curated sales,” Brooks said. “New buyers are in the market and they are much more open to buying masterpieces across categories.”

Postwar and contemporary art sales totaled 927.7 million pounds in the first half, up 16 percent, Christie’s said. Impressionist and modern art sales gained 43 percent to 771.6 million pounds. Old Masters continued their slump, falling 32 percent to 71.1 million pounds.

Almost half of the auction took place in the Americas -- particularly New York -- in the first half. The Americas accounted for sales of 1.4 billion pounds, up 35 percent from a year ago. Sales in Asia increased 16 percent to 294.2 million pounds.