* HSI -0.1 pct, SSEC -0.1 pct, CSI300 +0.1 pct
* HK property developers fall on news of UnionPay's tighter rules
* CNOOC jumps after profit beats estimate
SHANGHAI, March 24 (Reuters) - Hong Kong stocks drifted lower on Friday morning, with investors watching corporate earnings and a vote on a healthcare bill seen as President Donald Trump's first policy test.
China stocks were roughly flat, with gains in transport stocks offset by losses in energy majors .
In Hong Kong, the benchmark Hang Seng index dropped 0.1 percent, to 24,308.63 points at the end of the morning session. The main index has stayed largely flat this week.
The Hong Kong China Enterprises Index lost 0.2 percent, to 10,462.95 points.
Analysts worry that Trump's failure to pass the healthcare bill would cast doubt on his ability to deliver on the promises of tax cuts and infrastructure spending.
"We all have the same assumption. If he meets some obstacle here, he would also meet obstacles elsewhere," said Alex Wong, a director at Ample Finance Group. "There are concerns in the Hong Kong market, but not big enough to be overly anxious."
Wong noted investor appetite for risky assets remains solid, but wild swings may be seen in some stocks as earning reports start to trickle in.
Most sectors in Hong Kong lost ground, with resource stocks leading the declines.
Property developers lost 0.6 percent on news reports that China's biggest bank card provider UnionPay moved to tighten regulations over how mainland customers can use its debit and credit cards to purchase houses in Hong Kong.
Shares of index heavyweight CNOOC Ltd jumped about 4 percent, after the offshore oil and gas producer in China reported 637 million yuan ($92.4 million) in annual net profit for 2016, above the estimate of a net loss polled by Reuters.
In China, the blue-chip CSI300 index rose 0.1 percent, to 3,466.76 points, while the Shanghai Composite Index lost 0.1 percent, to 3,246.22 points.
The blue-chip index has gained 0.6 percent so far this week.
Most sectors advanced in China by the lunch break.
A gauge of consumer discretionary plays gained 0.6 percent by midday, after receiving a boost from industry bellwether Midea Group Co Ltd and Gree Electric Appliance Inc of Zhuhai.
($1 = 6.8933 Chinese yuan)
Reporting by Jackie Cai and John Ruwitch; Editing by Jacqueline Wong