LONDON — China surged clear at the top of the Olympic medals table on Sunday, adding two more golds to their opening day haul as swimming star James Magnussen put Australia on course for relay glory.

After dominating day one of competition with four gold medals, Chinese athletes hit paydirt once again with wins in shooting for Guo Wenjun before synchronised divers Wu Minxia and He Zi triumphed at the Aquatics Centre.

"I just focused on doing my best on the final shot," Guo said, adding: "I think everyone is good, I just never give up."

Elsewhere Sunday the women's gymnastics competition was rocked by a failed drugs test, as organisers launched a probe into rows of empty seats at venues.

It was Magnussen's first swim at the Games and the 'Missile' delivered on his brash confidence, clocking a sizzling 47.35 seconds to surge past Lezak (48.04).

Defending Olympic champions America were second quickest ahead of Russia and France.

"I felt nice and relaxed in the first 50 and I just let the crowd carry me home at the end," Magnussen said.

The Americans, who have won eight of the 10 Olympic gold medals awarded in the event, are expected to bring in big guns Nathan Adrian, Cullen Jones and Michael Phelps for Sunday night's final.

US teenager Missy Franklin, swimming in seven events, was second-quickest.

Galiulina underwent a drugs test on July 25, three days before the start of the women's artistic gymnastics competition.

Coe said unoccupied seats at some venues were due to accredited officials still working out which events to attend, but he said he had visited four events on Saturday which were full to capacity.

"Let us put this in perspective. Those venues are stuffed to the gunnels. The public are in there," Coe said.

"There are tens of thousands of people at this moment within the accredited 'family' that are trying to figure out what their day looks like, where they are going to be asked to go to, frankly working out how you divide your time."

Former world number one Novak Djokovic and home hope Andy Murray, who was knocked out of the doubles on Saturday, are also in action.

A total of 14 medals are up for grabs on Sunday, with two also on offer in judo and weightlifting, as well as one each in fencing and archery.