LONDON, July 29: Two world records fell in the pool on Sunday as China surged clear at the top of the Olympic medals table.

American Dana Vollmer won the women's 100m butterfly gold medal, clocking a world record of 55.98sec for a crushing victory over China's Lu Ying.

Vollmer became the first woman to break through the 56-second barrier as she added Olympic gold to the world title she claimed last year.

She bettered the previous world record of 56.06sec set by Sweden's Sarah Sjostrom on July 27, 2009 at the World Championships in Rome.

“I just relied on my strengths,” Vollmer said. “Just set it up well, passed a few people and charged it home.”

South African Cameron van der Burgh won the men's 100m breaststroke gold in a world record of 58.46sec.

Van der Burgh led the whole way for a dominant victory, improving the previous record of 58.58 set by Australian Brenton Rickard on July 27, 2009 at the world championships in Rome.

France's Camille Muffat won the women's 400m freestyle gold with Britain's defending champion Rebecca Adlington in third.

Overall, China had a commanding early lead in the rankings with nine medals, six of them gold, on the second full day of competitive sport.

They celebrated their burgeoning gold haul with victory in the 3-metre synchronised springboard which was won by divers He Zi and Wu Minxia with an inward 2-1/2 somersault.

For legendary diver Wu, it was her third consecutive gold medal in the 3m springboard synchronised after wins in 2004 and 2008.

An Kae Um won North Korea's first gold medal of the games in the women's judo 52-kilogram category. The 20-year-old An defeated Acosta Bermoy of Cuba in the final in a match that went into overtime.

Meanwhile, Organisers sought to quell growing public frustration on Sunday over empty seats across venues at the London Olympics.

The sight of rows of vacant seats at football stadiums, Wimbledon, the aquatic centre and beyond has angered Britons who tried and failed to buy tickets in the build-up to the Games after being told they had sold out.

More empty seats were reported on Sunday including at the equestrian dressage at Greenwich Park, despite the draw of Queen Elizabeth's granddaughter Zara Phillips making her Olympic debut.

Olympic organisers launched an urgent inquiry into the seating fiasco to nail down precisely who had not taken up their places and why and Organising chief Sebastian Coe, responding to the criticism, said the troops and students would fill the gaps.

Hundreds of fans wanting to see New Zealand, Brazil, Belarus and Egypt were stranded in London or forced to sit on the train floor Sunday as service operators supplied only two morning London-to-Manchester services in time for the noon kick-off of the New Zealand-Egypt match in Manchester, 200 miles (320 kilometres) northwest of London.

Heavy rain after a hot, dry spell on Sunday also put a dampener on outdoor events on the second day of full sporting contest, as did the announcement that Uzbek gymnast Luiza Galiulina was provisionally banned from the Games for a positive drugs test.

St. Kitts & Nevis sprinter Tameka Williams was sent home by her team for a potential drug violation. Williams had been using a substance which was “clearly outside the medical code,” St. Kitts Olympic committee vice president Dennis Knight said.

At Wimbledon in southwest London, the new retractable roof came in handy.

Maria Sharapova won her Olympic debut, beating Shahar Peer of Israel 6-2, 6-0 on the protected Centre Court, women's second seed Agnieszka Radwanska crashed out in a surprise first-round defeat by world number 24 Julia Goerges of Germany while Britain's Andy Murray and Serbia’s Novak Djokovic reached the second round.

Some 22 matches on other courts were postponed.

Day Two also saw the latest incarnation of the US basketball ‘Dream Team’, this time featuring LeBron James, Kobe Bryant and Kevin Durant, begin their title defence with a comfortable 98-71 win over France after a joyful display of high-flying skill.

In an important water polo preliminary, Serbia beat three-time defending champion Hungary 14-10 in a match between bitter pool rivals and medal favourites.—Agencies