The majority of U.S. businesses operating in Hong Kong are worried about the impact of the controversial national security law recently imposed on the city by China, according to a survey by the American Chamber of Commerce.

The lobby group said 76 percent of companies were concerned about the sweeping measures barring subversion, secession, terrorism and foreign collusion, with most being "extremely concerned.”

The poll of member companies — which AmCham described as a "temperature test” of members’ sentiments rather than a scientific study — received responses from 183 firms, more than half of which have headquarters in the U.S.