By Liana B. Baker and Yimou Lee

(Reuters) - Tencent Holdings Ltd <0700.HK> is nearing a $6.6 billion deal to buy a majority stake in Finland's Supercell Oy, a person familiar with the matter said, in what would be the biggest-ever purchase of a mobile games maker.

China's biggest social network and online entertainment company plans to buy the 73.2 percent stake in Supercell from Japanese media and telecoms company SoftBank Group Corp <9984.T>, valuing the maker of the popular mobile game 'Clash of Clans' at more than $9 billion, the person said, declining to be identified because the matter was confidential.

Analysts said through the deal, Tencent could enhance research and development capability and boost revenue in the world's largest mobile gaming market.

China's mobile gaming revenue is likely to grow 17 percent this year to 60 billion yuan ($9.11 billion), accounting for nearly a quarter of the world's total, according to market researcher TrendForce.

Known for investing in game developers through partnerships and minority stakes, Tencent owns 'League of Legends' developer Riot Games and has a stake in Activision Blizzard Inc <ATVI.O>, the owner of the 'Call of Duty' franchise.

Last year, it bought a 15 percent stake in mobile game developer Glu Mobile Inc <GLUU.O>, which developed the 'Deer Hunter' and 'Kim Kardashian: Hollywood' games, for $126 million in a move to expand in the U.S. gaming market.

Tencent's purchase of Supercell would surpass the previous record gaming acquisition in November, when Blizzard paid $5.9 billion for 'Candy Crush Saga' creator King Digital Entertainment.

"Tencent has weaker research and development capability and such a deal could help enhance it," said senior director of TrendForce Jeter Teo.

With Supercell's popular games, the deal could boost Tencent's mobile gaming revenue and attract more gamers to the company's ecosystem such as messaging app WeChat and social media platform QQ, said Marie Sun at Morningstar.

Online gaming has long been Tencent's main cash cow. The company reported a 43 percent revenue rise in the first quarter, aided by growth in its gaming and advertising businesses.

The company has enough funds for its latest acquisition. It had $8.6 billion in cash and cash equivalents and $2.9 billion in borrowings at the end of the first quarter. Just last week, it completed a $4.44 billion loan with 20 banks.

Tencent, which is in late-stage talks with SoftBank, is in discussions with several financial investors, including Hillhouse Capital Group, to join in the purchase as co-investors, the Wall Street Journal reported on Wednesday, citing people familiar with the matter. (http://goo.gl/XqrgZy)

An agreement could be disclosed as early as next week, the report said.

Tencent and SoftBank declined to comment, while officials at Supercell were not immediately available to comment.

A deal with Tencent will also mark the third major asset reshuffle by SoftBank in less than a month.

The Japanese media and telecoms company announced a plan earlier this month to sell $10 billion worth of shares in Chinese e-commerce giant Alibaba Group Holding Ltd <BABA.N> to cut debt, as well as a decision to sell its stake in GungHo Online Entertainment Inc <3765.T> back to the mobile game maker for 73 billion yen ($691 million).

SoftBank expects to book a profit of 200 billion yen to 250 billion yen ($1.89 billion to $2.36 billion) this financial year from the Alibaba share sale, which will reduce its stake in the Chinese firm to around 27 percent from 32.2 percent.

SoftBank said last year it had increased its controlling stake in Supercell to 73.2 percent, without disclosing financial details. Together with GungHo it had bought a majority stake in the mobile games maker in 2013 for about $1.5 billion.

($1 = 6.5840 Chinese yuan renminbi)

(Reporting by Arunima Banerjee in BENGALURU, Liana Baker in SAN FRANCISCO, Yimou Lee and Tris Pan in HONG KONG; Additional reporting by Elzio Barreto; Writing by Miyoung Kim; Editing by Shounak Dasgupta and Kenneth Maxwell)