The scary state of the subway has reduced even children to tears.

The first-ever “Haunted Subway” is underway at Union Square — and already it’s sent at least three of the systems youngest riders into hysterics, video shows.

The NYPD’s Transit District and MTA kicked off the two-day scarefest Thursday.

Footage from the opening night shows one transit worker in full uniform — with half of his face chewed off and bloodied. Another — a sergeant with the Anti-Crime Unit — is dressed up as Pennywise, the uber-creepy clown from Stephen King’s “It.”

NYPD officers were on hand to console the clearly shaken thrill-seekers as they poured out of a pitch-black room, which is divided into sections like a maze.

“This is not a terrifying, horrifying experience but for a child, it could be scary,” NYPD Sgt. Carlos Nieves told The Post Friday, adding that kids are warned beforehand. “Most kids were really into it and came out laughing.”

The “Haunted Subway” is located closest to the 15th St. subway entrance and continues Friday from 4 to 7 p.m.

Children under 7 must be accompanied by an adult for the roughly minute-long spectacle.

“We talk to them and say, listen, everything in there is not real,” said Nieves. “It’s just trying to have fun on Halloween. All the people dressed up in there are police officers.”