Macau's casinos lost around $14 billion in value on Wednesday (September 15) amid a sweeping regulatory overhaul.
The revamp could see officials supervising companies in the world's largest gambling hub.
With Macau's lucrative casino licenses up for rebidding next year, a government proposal to revise the city's gaming law spooked the Hong Kong market, with operator stocks tumbling by as much as a third.
Wynn Macau led the plunge, falling as much as 34% to a record low, followed by a 28% tumble for Sands China.
Peers MGM China, Galaxy Entertainment , SJM and Melco Entertainment all fell heavily, bringing the drop to $14 billion.
Beijing, which is increasingly wary of Macau's reliance on gambling, has not yet indicated how the license rebidding process will be judged.
Macau's secretary for economy and finance, Lei Wai Nong, announced late Tuesday (September 14) a 45-day consultation on the gambling industry to begin the following day.
He said there there were still some deficiencies in industry supervision.
At a press briefing, Lei detailed nine areas for the consultation, including the number of licenses to be given, increased regulation and protecting employee welfare.
Government representatives may also be brought in to supervise day-to-day operations at the casinos.
Discussions over the future of Macau's licenses comes amid increasingly rocky U.S.-China relations, leaving some investors fearing that U.S.-based casino operators may not fare as well as local players.