Lam, addressing reporters after a long weekend of more turmoil, said tourism arrivals were down by half and that hotels and retailers were suffering.
Hong Kong's third quarter economic data will definitely be "very bad", Lam said.
Lam said she did not have the data with her. But empty streets and tourist attractions are evidence of the fallout from the massive protests that began over proposed legislation that could have led to Hong Kong residents facing trial in mainland Chinese courts. Lam eventually dropped the legislation.
Initially, the protests caused little damage and were confined to an area near Hong Kong government offices. But they've since spread to many parts of the former British colony, which enjoys freedoms guaranteed to the semi-autonomous region of about 7 million people when Beijing took control in 1997.
The demonstrations have become increasingly violent, with protesters targeting shops and banks.
The city's airport has been periodically besieged by protesters, and some train and subway lines and shopping malls have suffered significant disruptions from the demonstrations.
So far, Hong Kong's stock exchange has kept steady. The benchmark Hang Seng index gained 0.5% on Tuesday. Prices have been supported by ample demand since shares listed in Hong Kong are perceived as being relatively cheap, says veteran investment manager Francis Lun.
The city's monetary regulators say Hong Kong has ample reserves to weather bouts of hard times.
But tourism and retailing are languishing, and some investors are shifting money out of the city, Lun says
Analysts say the political turmoil and the risk of intervention by Beijing could undermine Hong Kong's status as a world financial hub.
"Unless it stops soon...it's really Hong Kong's survival at stake," he told The Associated Press.
Protesters are demanding Lam's resignation even after she withdrew legislation that provoked the latest rounds of turmoil. They also want investigations into the handling of the protests by police.