Hong Kong stocks tumbled 2.73 percent on Friday, with airlines the hardest hit, following an outbreak of bird flu in mainland China which has killed six people.
The benchmark Hang Seng Index fell 610.59 points to end at 21,726.90 -- a four-month low -- on turnover of HK$77.22 billion ($9.96 billion).
Shanghai was closed for a public holiday.
Travel and leisure-related firms were hit on news of the outbreak of the H7N9 strain of bird flu.
Authorities in Shanghai on Friday ordered the closure of all live poultry markets in the city and culled more than 20,000 birds to curb the spread of the deadly virus.
In all, there have been 14 confirmed human infection cases, including the dead.
The news hurt the aviation sector, with China Southern Airlines losing 8.5 percent to end at HK$3.87, while China Eastern Airlines fell 8.3 percent to HK$3.10 and flag carrier Air China tumbled 9.8 percent to HK$6.05.
"With more human infections by the bird flu, some leisure travellers may try to avoid travelling... particularly to China," Davin Wu, an analyst at Credit Suisse, told Dow Jones Newswires.
And Jackson Wong, investment manager at Tanrich Securities, said: "The cases of H7N9 bird flu are rising and the death rate is high. Suddenly we've got a number of uncertainties at hand."
However, Core Pacific-Yamaichi head of research Castor Pang said he thought the concerns were overblown.
"Investors are pricing in a scenario under which there will be an outbreak which will severely hurt the airlines' earnings," he said. "We simply don't know if that's what will happen."
Adding to selling pressure is unease about US non-farm payroll figures due out later on Friday, with expectations low after a disappointing report on jobless claims Thursday, which unexpectedly rose for the week ending March 30.
The results come a month after huge federal spending cuts came into force at the beginning of last month.