Besides meaning "nine, nine", "jiu, jiu" in Chinese also means "for a long time," thus making Wednesday an auspicious day to get married.
The fact that another nine is added for 2009 has only made the day luckier in the world's most populous nation, state press reported.
"We were going to get married in March, but when we looked at the calendar and saw September 9, we changed our minds," a young man surnamed Yang said on Beijing television as he queued at a local marriage office.
"We have been waiting in line all night," he said as his bride-to-be held his hand and smiled.
As of late Tuesday, 3,500 couples had made online bookings to marry in three Beijing districts, while nearly 5,000 couples had made advanced bookings in the country's biggest city Shanghai, said the China News Service.
In the southern metropolis of Guangzhou, more than 6,100 couples had registered to marry on Wednesday, while numerous large Chinese cities each reported wedding totals of at least 2,000 couples, the report said.
Officials were expecting many more newlyweds-to-be to crowd into marriage offices than those who had pre-registered, it said.
The number tying the knot in China was expected to surpass the number of couples who married on August 8, 2008 -- the number eight is traditionally considered lucky, while it also sounds like the word for wealth.
On 08/08/08, 16,400 couples applied for marriage registration in Beijing alone, press reports said at the time.
By comparison, there was a total of 170,000 marriages in Beijing in the whole of 2006, a 25-year record, the reports said.
Over 500 Malaysian couples tied the knot at a Buddhist temple on Wednesday, in a mass wedding held on the auspicious "999" date which signifies hopes for a long-lasting marriage.
"I chose this date '999' as it signifies everlasting love," construction supervisor Thomas Wong, 30, said as his new bride, 25-year-old accountant Ivy Tan, stood by his side.
"I hope to give my wife a memorable wedding, it's once in a lifetime we get these auspicious numbers," he told AFP at the Thean Hou temple in the capital Kuala Lumpur.
A spokesman at the temple said the last biggest mass wedding was on August 8 last year, or '888' which is also deemed good luck in Chinese numerology as '8' can mean "prosperous".
"We had 470 couples then and this year we have 556 -- I believe this is the largest mass wedding in the country so far," organiser Kong Cher Peng said.