China's Liu Xiang plans to celebrate his birthday by sending a warning to his Olympic 110m hurdles rivals on his first appearance at the London Grand Prix tonight.

Liu, a former Olympic champion, is among the leading contenders to win gold at the London Games and he has the perfect opportunity to underline his credentials in the Diamond League meeting at Crystal Palace.

The Chinese star, who leads the world rankings this year with 12.97 seconds, won the Olympic title in Athens in 2004, but left fans devastated when he pulled out of the Beijing Games because of an Achilles injury.

Liu, who turns 29 today, has continued to struggle with injury since Beijing, but he believes he is back to his best after opting for a new stride pattern.

Now, just two weeks before the Games begin, Liu, who also won gold at the 2007 World Championships, hopes to fine-tune his Olympic preparations with victory over outdoor world champion Jason Richardson and world indoor 60m hurdles champion Aries Merritt.

"This will be my last race before the Olympics so I will be looking for a very strong performance. The London Diamond League will be the perfect race for me to complete my preparation," Liu said.

"I'm really excited to be competing in London for the first time. It's a great opportunity for me to experience the conditions and atmosphere of the host city just two weeks before the Games."

On track for success

After two impressive wins in the Diamond League events in Shanghai and Eugene this year, Liu is hopeful he is on track for success at the Olympics, where his main rival will be Cuban Olympic champion and world record holder Dayron Robles.

"My form has been good so far this season and my preparation is on target," Liu added.

"The line-up at the London Diamond League is tough and running against world class athletes in Olympic conditions will be a good test for me.

"I really enjoy racing in the UK, although I have not had many chances in my career. Hopefully I will have a lot of support from the Chinese community."

With 16 Olympic and 15 reigning world champions taking to the track today and tomorrow there are plenty of intriguing events, but the main highlight will be the 100m clash between injury-prone duo Tyson Gay and Asafa Powell.

The second and third fastest men of all time will take to the track in south London hoping to prove they still have Olympic gold medal potential despite the dominance of Usain Bolt and Yohan Blake.

American star Gay won the US trials last week in a respectable 9.86 seconds, while Powell, the former world record holder, finished third behind Blake and Bolt in the Jamaican trials.

While Blake and Bolt look to be in a league of their own - clocking 9.75 secs and 9.76 secs this year - Gay and Powell are determined to lay down markers of their own in London.

"I haven't raced much this year and I'm feeling better each time out there on the track," Gay said.

"My body is getting closer to where I want it to be. I've shown over the years that through all of the injuries, I'm a fighter, and I hope to be fighting for that Olympic gold in London later this summer."

Powell, 29, added: "This is a big year for me. I'm not getting any younger but there's a lot more to come from me. I'm looking forward to taking on Tyson. It's good to have him back and it's going to make for a very competitive Olympic Games."