* Q4 net profit 20.8 bln yuan vs 16.9 bln analysts' estimates
* WeChat hits 1 billion users, 580,000 mini-apps
* Investments brought in gain of 20.14 bln yuan in 2017
* Plans "aggressive" investment in 2018 (Adds detail, management comment)
HONG KONG, March 21 (Reuters) - Chinese internet giant Tencent Holdings will step up investments in areas such as video, payment and artificial intelligence, it said after reporting better than expected quarterly net profit thanks to a string of successful IPOs.
With a market capitalisation of about $560 billion, Tencent is Asia's most valuable listed company and the world No.5 behind Apple, Alphabet, Amazon.com and Microsoft.
"The year of 2017 was really a stellar year for Tencent. Many of the achievements are the result of investment we made years ago," the company's president, Martin Lau, said at a media briefing in Hong Kong.
"This demonstrates the importance of forward-looking investment. Therefore, for the year 2018, we are planning to step up our investment in a number of key areas."
The areas earmarked for further investment include video, Weixin Pay, cloud services, artificial intelligence and smart retail, he said. Lau added that the company would "aggresively" acquire video content and subsidise payment adoption, which could hurt margins in the short run.
Net profit for the three months to Dec. 31 nearly doubled year on year to 20.8 billion yuan ($3.29 billion), China's largest social media and gaming company said in a filing to the Hong Kong Stock Exchange.
A 51 percent jump in revenue was weaker than expected after mobile gaming revenue growth slowed from the previous quarter, but the company said overall revenue was supported by payment-related services, advertising and digital content subscriptions and sales.
Tencent's messenger-to-payment app WeChat now has more than 1 billion users and has launched in-app services that could erode Apple and Googles app revenue.
There are now 580,000 of these mini-programmes, it said, with more than 170 million daily active users as of January.
The group's successful initial public offerings (IPOs) included Yixin, Netmarble, ZhongAn Insurance and Sogou, it said, helping it to register gains totalling 20.14 billion yuan last year, up from 3.59 billion yuan in 2016.
Lau said that music subsidiary Tencent Music is another IPO candidate but the company had no plans to spin off other wholly-owned units at the moment.
Chief Executive Pony Ma said Tencent would consider an A-share listing in Shanghai when conditions are right.
Tencent's wealth management platform LiCaiTong had more than 300 billion yuan of assets under management as of January, while its consumer loans business Weilidai managed loans of more than 100 billion yuan at the end of 2017, it said.
Chief strategy officer James Mitchell told reporters the company was not too concerned about tightening scrutiny of Chinese investments by the U.S. government because most of Tencent's overseas investments are for minority stakes in non-sensitive sectors and spread across the world.
Asked what the company does to avoid a Facebook-style data privacy breach, president Lau said that Tencent has strict protection measures to ensure users' data privacy and that WeChat's operation in China has to comply with local laws and regulations.
Tencent's Hong Kong-listed shares have risen 14 percent so far this year, outpacing a 5 percent rise in the benchmark Hang Seng Index. ($1 = 6.3304 Chinese yuan renminbi) (Reporting by Sijia Jiang Editing by Muralikumar Anantharaman and David Goodman)