Chinatown has become overrun with vagrants, many of them menacing, residents and workers said in the wake of Saturday’s Bowery bloodbath.

“Something is going on, something is just in the air and there are just a lot more mentally unstable people around. There are a lot more crazies around,” said the manager of an East Broadway restaurant.

Another merchant, Eric Lee, manager of Dim Sum Go Go, said in the last year the number of homeless in Kimlau Square, the neighborhood center near where the murders happened, has more than doubled, from about four to more than 10.

“They’re sleeping here — on mattresses, benches, They’re hanging out here, drinking, smoking. Overnight. It’s not good. It affects our business. They drink a lot, they get rowdy and loud,” Lee said.

Karlin Chan, a member of the local community board and longtime Chinatown activist, said the homeless using city parks as their bedrooms and bathrooms has been a major concern.

“I go out at 5:10 in the morning and carry a flashlight just to watch out for the excrement,” he said. “We are not talking dog doo doo. I have seen them just lean off the bench and go No. 2.”

Many expressed frustration that the city was not doing enough to stem the crisis.

“This senseless and devastating act of violence against the most vulnerable members of our community must serve as a wakeup call: we must do more than the bare minimum to help the tens of thousands of New Yorkers in our homeless shelters and on our streets,” said City Councilwoman Margaret Chin who represents the area.

William Bray, the president of the 5th Precinct Community Council, said complaints about the proliferation of homeless were a staple at the group’s monthly meetings.

“The cops, unfortunately, their hands are tied,” he said. “With City Hall, there’s only so much they can do.”

Wellington Chen, executive director of the Chinatown BID, said a convenience store on the western end of Chinatown — where the homeless have been historically caused more of a problem — resorted to hiring off-duty NYPD officers to chase off panhandlers.

Mary Loriggio, owner of Luna Pizza on Park Row across the street from Kimlau Square, said she has watched as the number of homeless has grown in recent years and even gives them free pizza so they don’t hang around her shop.

“The mayor needs to do something about this. They need to help the homeless people,” Loriggio said. “We need to focus on the people here before we focus on anything else. He needs to focus on the people here.”

Additional reporting by Kevin Fasick