Macau casino shares yesterday plunged as the Chinese territory embarked on a week-long lockdown to curb its worst COVID-19 outbreak, while neighboring Hong Kong said it was mulling a mainland-style health code system. Share prices of six gaming conglomerates — Sands China, Galaxy Entertainment, SJM Holdings, Melco International, MGM China and Wynn Macau — fell by between 6 and nearly 9 percent in yesterday morning trade. It is the first casino lockdown in more than two years, overriding a previous deal between the industry and the Macau government that only those found with infections would need to close temporarily. Photo:…