An eagle-eyed subway rider spotted a skimming device on a MetroCard machine in Manhattan, sparing other straphangers from bank and credit card fraud.

Cops said the device was installed at the Columbus Circle station sometime on Wednesday, but it was not clear yet how many riders’ accounts could have been affected.

The vigilant straphanger spotted the black skimmer about 9:30 p.m. Wednesday at a machine on the downtown 1 platform, and thought it looked suspicious. He took it out, and gave it to a station agent.

A pinhole camera was then discovered inside a fake wall socket above the machine.

Transit workers are now checking every machine in the subway system for other devices.

The MTA wants all riders who purchased a MetroCard through that machine to immediately check their bank and credit cards for any fraud.

“We continue to ask our customers if you see something, say something,” said New York City Transit president Carmen Bianco. “Particularly if they notice any suspicious activity or device in our system.”

The authority will also launch a campaign to remind customers to be careful when they purchase MetroCards, and be on the lookout for skimmers.

It was not immediately clearly how many riders could have had their financial information compromised, but the NYPD is investigating.

Anyone with information should reach out to Crime Stoppers at 1.800.577.TIPS.

Last week, technicians discovered a scanning device and camera at a ticket machine at the LIRR station in Baldwin, Long Island.

Vasile Ovidiu Haidau, 35, of Romania is suspected of installing that device, and has ties to a credit card-identity theft gang in California.

Tipsters should call MTA Police detectives at 516.222.6501, according to an LIRR spokesman. He is considered to be dangerous.