* Hong Kong leads global IPO rankings with $22.4 bln
* China Tower is world's biggest IPO in 2 years, raising $6.9 bln
* Recent notable HK floats have struggled on debut
HONG KONG, Aug 7 (Reuters) - Hong Kong is readying to host the world's biggest initial public offering (IPO) in two years on Wednesday, as China Tower Corp Ltd debuts in a market with record IPO numbers but where recent floats have struggled to maintain issue prices.
The world's largest operator of mobile telecommunications towers last week priced its shares at HK1.26 each, the bottom of its indicative range, to raise $6.9 billion.
That took the amount raised by companies listing in Hong Kong in 2018 to $22.4 billion, in the city's best performance by this point in the year, showed data from Thomson Reuters. That makes it the world's leading center for capital raising, ahead of second-placed New York Stock Exchange at $20.6 billion.
However, China Tower's IPO comes just weeks after other notable deals struggled upon debut.
Chinese smartphone maker Xiaomi Corp suffered a weak debut in early July after raising $4.7 billion. The stock recovered to trade as much as 30 percent above its IPO price but has since slipped to just 1.2 percent higher at $17.22.
Earlier this month, Ascletis Pharma Inc became the first firm to list under new rules for biotech startups, having raised $400 million. Its shares began trading on Wednesday but had fallen as much as 31 percent by Friday. On Monday, they were trading at HK$10.9, down 22 percent from their issue price.
"Stocks like Xiaomi which aimed for a higher valuation, and Ascletis, which is seen a lead for biotechs in testing valuation, both failed to impress and that will make it harder for upcoming IPOs to take any aggressive approach in pricing," said Steven Leung, a sales director at broker UOB Kay Hian.
Nasdaq-listed Beigene Ltd will become the second biotech to list under the new rules when it floats on Wednesday after raising $903 million.
Market participants said broader market weakness has not helped, with investors fretting over the potential impact of Sino-U.S. tit-for-tat import tariffs. The benchmark Hang Seng share price index has lost 3.5 percent since the start of July.
"Particularly strong risk appetite is required for IPOs in the current climate," said Alex Wong, a director of asset management at Ample Capital.
This year, 159 firms have applied to list on the Hong Kong stock exchange's Main Board, putting 2018 on course to be the IPO market's busiest year in at least a decade, showed data from bourse operator Hong Kong Exchanges and Clearing Ltd.
However, no Hong Kong stock currently features in the year's top 20 first-day IPO gains worldwide.
Of firms selling over $500 million worth of shares, payments processor Adyen NV jumped 90 percent on its Amsterdam debut in June, showed data from Dealogic. Online flea market operator Mercari Inc added 77 percent on its first day in Tokyo.
(Reporting by Jennifer Hughes and Donny Kwok Editing by Christopher Cushing)