Seven people who "seemed to be under the influence of something" outside Penn Station were rushed to the hospital Friday night, according to an FDNY spokesperson.

One person is in serious condition, four are serious but stable, and two have minor injuries, the spokesperson said.

Though authorities could not confirm the cause of the hospitalizations, sources who spoke with PIX 11 believe the group of people became ill after smoking K2 — a cheap, highly-addictive synthetic drug known to cause anxiety, paranoia, hallucinations, vomiting, violent behavior, and other ills, according to the NYC Department of Health.

Made by spraying chemicals on dry leaves, the drug reached epidemic levels two years ago, before Mayor de Blasio signed legislation intended to toughen laws against the K2 "scourge."

Still, overdoses caused by the synthetic substance soared in New York last summer, with 130 people hospitalized after smoking the drug in just a three-day span. That mass overdose incident came after the city said that K2-related ER visits had decreased 85 percent since their peak in July 2015.

More recently, a batch of K2 sickened 40 people — at least 12 of whom were reportedly foaming at the mouth — in Newark, New Jersey. And earlier this week, dozens of people were hospitalized near Newark's Penn Station, with police eyeing K2 as a possible cause.

There have been two confirmed deaths caused by K2 in New York City, according to the health department.