* Sunshine 100 plunges as much as 21.3 pct, Haichang down 16.3 pct in debut
* Weak investors' demand for both deals weigh on shares (Adds Hang Seng index, retail investor demand for recent IPOs in Hong Kong)
HONG KONG, March 13 (Reuters) - Shares in a Chinese theme park operator and real estate developer sank at least 16 percent in their Hong Kong debut on Thursday as worries about the weakness in China's economy left the overall stock market trading around a one-month low.
Haichang Holdings, which operates amusement parks in China, fell to as low as HK$2.05($0.26)compared to an initial public offering price of HK$2.45 a share. The benchmark Hang Seng index, by comparison, edged 0.5 percent higher, after closing at its weakest level since Feb. 10 on Wednesday.
Sunshine 100 China Holdings Ltd, a real estate developer backed by U.S. private equity firm Warburg Pincus , fell as low as HK$3.05 compared with its HK$4.00 per share IPO price.
Jittery investors are avoiding risky assets ahead of a batch of data that may offer clues about the extent of China's economic slowdown. Chinese Premier Li Keqiang told reporters on Thursday that the economy faced serious challenges this year.
Retail and institutional investors had shown tepid demand for both stocks during the IPO process, in contrast to the massive rush seen for some offerings earlier this year that spurred some shares to log double-digit gains as they started trading.
Analysts said investors may have started to show "IPO fatigue" as 17 companies have listed in Hong Kong so far this year, raising $4.7 billion, according to Thomson Reuters data.
The $258 million IPO for Sunshine 100, a commercial and residential real estate developer in second and third-tier Chinese cities, saw retail demand just 0.6 times the number of shares on offer, compared with deals that were oversubscribed more than 1,000 times just last month.
The retail portion of Haichang's deal generated 4.65 times more orders than the shares on offer, while its institutional tranche was moderately oversubscribed, the company said in a securities filing on Wednesday.
Night club operator Magnum Entertainment Group Holdings Ltd's saw the highest ever level of oversubscription for a Hong Kong IPO. It listed in January after it was more than 3,000 times oversubscribed.
Pork producer Huisheng International Holdings Ltd had the second-highest ever level of oversubscription, with retail investors generating demand 2,188 times more than orders in February.
Pork producer Huisheng International Holdings Ltd had the second-highest ever level of oversubscription, with retail investors generating demand 2,188 times more than orders. ($1 = 7.7659 Hong Kong Dollars) (Reporting by Elzio Barreto; Editing by Paul Tait and Miral Fahmy)