(CNN) The New York City Police Department is warning Brooklyn residents about a "particularly toxic" batch of synthetic marijuana known as K2 that has caused nearly 50 overdoses since Friday.

NYPD Chief of Department Terence Monahan issued an advisory alert for residents in five affected areas in Brooklyn.

In a statement, police said there had been 49 overdose cases linked to K2 since May 18.

Of those, 15 were in the vicinity of Broadway and Myrtle Avenue, 21 at an address on Fulton Street, seven on Ralph Avenue, two on Sinderen Avenue and four on Atlantic Avenue. Websites for at least three of the addresses given by police say they are locations for shelters for the homeless.

"K2 is a dangerous, deadly drug, but this strain is especially threatening. All residents who live near these five locations are warned about exceedingly dangerous K2 batches in circulation, and advised to avoid usage," Monahan said. "Residents are urged to call 911 immediately if they or someone they know are showing symptoms of overdoses."

Advisory alert warning people about a particularly toxic batch of K2 that has triggered 49 overdose cases originating at five locations in #Brooklyn. More information here: https://t.co/WUcM0ufUpC pic.twitter.com/eqDnvW9AAg — Chief Terence Monahan (@NYPDChiefofDept) May 22, 2018