Serena Williams said on Friday she was not the greatest ever women’s tennis player after securing the year-end world number one ranking for the third time in her glittering career.

But the 32-year-old American power-hitter, now on a career total of 55 titles with 17 major wins, told reporters in Beijing ahead of the China Open that she was “maybe top five”.

Williams achieved the feat in 2002 and 2009, and joins Justine Henin and Martina Hingis as a three-time year-end number one, with only Steffi Graf (8), Martina Navratilova (7), Chris Evert (5) and Lindsay Davenport (4) ahead of her.

“I’m not the greatest player. I’m still playing and I’m still trying to reach records. And people like Steffi and Chris Evert and Martina Navratilova and Margaret Court, they are the greatest,” she said.

“Maybe top five, but definitely not number one. For me it’s an honour to even be mentioned amongst those amazing ladies.”

She is the top seed in the $US5,185,625 ($A5.57 million) China Open, while home favourite Li Na is seeded fourth.

The 2011 French Open winner comes into the tournament after a surge in form which has seen her become the first Asian player to reach the US Open semi-finals earlier this month.

31-year-old Li also received a boost with the news that she has became the fifth player to qualify for the $US6 million ($A6.44 million) end-of-season WTA Championships.

The world number five booked her place in next month’s grand finale in Istanbul featuring the top eight women’s players on Friday, the tennis organisation announced on its website.

Li is aiming for her biggest win on home soil when she takes on a star-studded field at the dual ATP and WTA event at Beijing’s Olympic Park.

However, she faces a tough route to the final, where she could meet her US Open semi-final opponent Williams.

Li faces Slovakia’s Daniela Hantuchova in the opening game, and could potentially face in the third round William’s older sister Venus.

The seven-time Grand Slam singles champions’ ranking slumped to 63rd after two years of illness and injury problems, but she has been in resurgent form lately, reaching the semi-finals of the Pan Pacific Open in Tokyo before crashing out in a close-fought match on Friday.

Venus Williams has a bye in the first round in Beijing, while her sister faces Russia’s Elena Vesnina.

Rafael Nadal and Novak Djokovic headline the men’s draw in Beijing, but no information was available from tournament organisers of the men’s schedule.