Last year, 28 million mainland Chinese visitors came to Hong Kong, a city of just 7 million residents. Such tourists come to shop for luxury goods, buy property and even give birth, embittering locals who feel they are being priced and crowded out of their own homes and subways.

"Hong Kong has become very crowded, very stuffy. We're losing our living space," said Roy Tam, president of environmental group Green Sense. Mr. Tam said he marched to the city's immigration department Tuesday with a few dozen others to protest the scheme's expansion. In the city's main shopping districts, he said, there are "no longer stores for Hong Kong people," only jewelry and luxury stores catering to Chinese shoppers.

Hong Kong Chief Executive Leung Chun-ying has tried to soothe fears about the plan, saying that the government will ensure adequate facilities to support the growth in tourism. Mr. Leung also said Tuesday that the government would control the number of people allowed to enter Hong Kong's borders, though his office declined to elaborate on his comments.

Last year, visitors to Hong Kong spent a combined $263 billion. Mainland tourists, who make up two-thirds of all visitors toHong Kong, are an economic lifeline for the city, where the tourism sector employs 6% of all residents.