* HSI +0.5 pct, H-shares +1.3 pct, CSI300 +1.1 pct
* China stocks bounce back on stimulus hopes
* Hong Kong casino stocks fall
By Natalie Thomas
BEIJING, May 8 (Reuters) - China shares are headed for their biggest one-day gain in a month on Thursday, as investors bet on further stimulus measures after the central bank warned of a deepening economic slowdown.
Hong Kong stocks also gained, aided by strong oil and gas shares, though overall increases were limited by sliding casino firms after China initiated a probe into illegal payments in Macau.
By midday, the CSI300 index of the largest Shanghai and Shenzhen A-share listings was up 1.1 percent, while the Shanghai Composite Index was also up 1.1 percent at 2,032.41 points.
The Hang Seng Index was up 0.5 percent at 21,863.95 points. The China Enterprises Index of the top Chinese listings in Hong Kong gained 1.3 percent.
The SSEC and CSI300 indexes registered their strongest one-day gains since April 10, as speculation intensified that government support for the flagging economy might be on the way after the People's Bank of China warned of the possibility of a further growth slowdown in a report on Tuesday.
"While nobody is certain how the government will actually act, investors widely believe economic conditions and corporate earnings will weaken further without strong official support and that psychology sparked a buying spree today," said Zheng Weigang, a senior trader at Shanghai Securities.
Property stocks were the biggest movers, after several companies with exposure to Beijing and the northern province of Hebei, including Hua Yuan Property Co Ltd and Metro Land Corp Ltd, hit daily trading limits of 10 percent, after the regions unveiled measures to aid the market.
Shijiazhuang, the capital of Hebei province, released a set of proposals to speed up plans for the development of a mega-metropolitan area encompassing Beijing, Tianjin and Hebei province on Wednesday.
"This would make it a major city within the Beijing Tianjin Hebei metropolitan area, so mid-level stocks with exposure to Hebei are going up," said Tian Weidong, head of research in Kaiyuan Securities in Xi'an.
Investors were also reacting to reports in the Chinese media that Beijing would no longer allow for land expropriation for commercial development within its fifth ring-road, said Wang Xiaojun, a strategist at Cinda Securities Co Ltd.
In Hong Kong, energy shares drove movement on the HSCE after data from the China Petroleum and Chemical Industry Federation showed faster growth in investment in the first quarter of 2014.
By the lunch break, China Petroleum and Chemical Corp (Sinopec) and PetroChina Co Ltd were both up 2.1 percent.
But gains on the Hang Seng were limited by a slump in casino stocks after China's state-backed UnionPay announced fresh measures to crack down on illegal payment channels in the world's largest gambling hub.
Shares in Galaxy Entertainment Group Ltd fell 8.4 percent, while Sands China Ltd fell 7.3 percent. Wynn Macau Ltd dropped 8.2 percent., (Additional reporting by Lu Jianxin in Shanghai; Editing by Jacqueline Wong)