More than 30 people became ill in an apparent mass drug overdose on a New York City street corner, sparking warnings from police and health chiefs.

Calls started coming in late yesterday that numerous people appeared to be overdosing in the Bedford-Stuyvesant neighbourhood of Brooklyn.

Witnesses reported seeing victims lying on the pavement, shaking and leaning against trees and fire hydrants.

Thirty-three people were taken to hospital with non-life-threatening injuries, police said. It was not immediately clear what drugs the victims had ingested, but police said some of the victims had been smoking K2, also known as synthetic marijuana.

Dennis Gonzalez, of Bushwick, told WNBC-TV that K2 use in that part of Brooklyn was out of control.

"It's gotten out of hand," he said. "They even sleep in the street, we have to walk around them. It's just too much to keep under control."

The Health Department said it "recorded a spike in K2-related emergency room visits" connected to the incident in Brooklyn. The department said it was investigating and monitoring casualty departments across the city.

"We remind New Yorkers that K2 is extremely dangerous," the Health Department said.

"The city's public awareness efforts and aggressive enforcement actions over the past year have contributed to a significant decline in ER visits related to K2."

Although K2 affects the same area of the brain as marijuana, it contains chemicals made in laboratories and sprayed on to dry leaves. These chemicals are not derived from the marijuana plant, according to the Health Department.

K2 can cause extreme anxiety, confusion, paranoia, hallucinations, rapid heart rate, vomiting, fainting, kidney failure and reduced blood supply to the heart.

The production and sale of the drug was outlawed in New York City last October.