WASHINGTON, DC - March 16: The entrance to the Metro Center station is gated closed during the morning rush hours on March 16, 2016 in Washington, DC. Metro's General manager Paul Wiedefeld made the decision to close for 29 hours for a safety inspection after a recent fire. Metro makes approximately 725,000 trips per day in the D.C. Metro area. (Photo by Pete Marovich/Getty Images)
PHOTO: Pete Marovich/Getty Images
WASHINGTON, DC - March 16: The entrance to the Metro Center station is gated closed during the morning rush hours on March 16, 2016 in Washington, DC. Metro's General manager Paul Wiedefeld made the decision to close for 29 hours for a safety inspection after a recent fire. Metro makes approximately 725,000 trips per day in the D.C. Metro area. (Photo by Pete Marovich/Getty Images)
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Story highlights

NEW: Washington Mayor Muriel Bowser said she learned of the shutdown late Tuesday afternoon

NEW: Metro riders react to shutdown with a mixture of humor and trepidation

Metrorail system will shut down for safety inspections until 6 a.m. Thursday

The closure comes after an electrical fire in a Metro tunnel on Monday

(CNN) —  

The entire Metrorail system in the nation’s capital will be shut down until Thursday morning for safety inspections of hundreds of electrical cables, officials said Tuesday.

The unprecedented closure, starting at midnight Tuesday, comes after an electrical fire in a Metro tunnel one day earlier caused the shutdown of three subway lines, said Paul J. Wiedefeld, the system’s general manager and CEO. The early-morning electrical fire involved a cable in the tunnel outside McPherson Square station.

The system shutdown is the first that is not weather-related. All six Metrorail lines and all 91 stations will close normally at midnight and remain closed until 5 a.m. Thursday.

Jack Evans, Metro’s chair, said the closure will have a major impact on regional travel.

“Without Metro, it’s going to have a lot of congestion,” he said. “It’s going to be very difficult, we recognize that, for people to get into work, for children to get to school, for everyone who relies on Metro, but safety is paramount. We need to get to the bottom of this.”

Preliminary findings of the cause of Monday’s blaze “show commonalities” with another cable fire last year, Wiedefeld said.

“While the risk to the public is very low,” he said, “I cannot rule out a potential life safety issue here and this is why we must take this action immediately.”

In last year’s fire, one passenger died after smoke filled the L’Enfant Plaza metro station in downtown Washington. A total of 84 people were treated by local hospitals, according to emergency officials.

“The investigation into yesterday’s cable fire at McPherson Square is ongoing,” Wiedefeld said. “As a preliminary matter, the conditions appear disturbingly similar to those in the L’Enfant Plaza incident of a year ago, and our focus is squarely on mitigating any risk of a fire elsewhere on the system.”

After the L’Enfant Plaza fire, the National Transportation and Safety Board released a statement saying “an electrical arcing event” sparked the incident.

“There was an electrical arcing event involving the trackside power cables (the third rail),” said a statement from the NTSB’s Peter Knudson.

On social media, Metro riders reacted to the shutdown with a mixture of humor and trepidation.

Alex Morash tweeted a GIF of zombies breaking through a wooden fence with the message: “Minor crowds expected for taxis and ubers tomorrow with #wmata shutdown.”

Greg Gadren asked, “So wait, #wmata is so unsafe we need to shut it down tomorrow, but it’s ok to take it home tonight? #fireeveryone”

The inspections of about 600 “jumper cables” will occur along all tunnel segments on the Metrorail system.

Washington Mayor Muriel Bowser told reporters that she was “shocked” by news of the shutdown, and only learned of it during a late-afternoon phone call from the chair of the Metrorail board.

Bowser said schools, government offices and businesses in the nation’s capital will open on Wednesday.

“Metro is operated by a compact,” she said. “We pay a lot of money, along with Maryland and Virginia, to operate a safe and reliable public transit system … We are a customer of Metro and we expect the to deliver for us in a safe way.”

The U.S. Office of Personnel Management said in a statement that federal agencies will also open, with employees able to perform “telework” from home or put in for unscheduled leave.

U.S. Transportation Secretary Anthony Foxx noted the Washington Metropolitan Area Transit Authority’s “long, well-documented list of safety issues,” according to a statement. He said, “They are doing the right thing by putting the safety of their passengers and workers first.”

“I’ve said it before, and I’ll keep saying it until the region takes real ownership of its safety oversight responsibilities: D.C., Maryland and Virginia need to stand up (for) a permanent Metro safety office with real teeth,” Foxx said. “What are folks waiting for?”

Foxx has urged Washington, Maryland and Virginia to establish a federally compliant safety oversight agency to oversee rail operations, according to letters released Tuesday by his office. Foxx called the current Tri-State Oversight Committee created by the three jurisdictions “an utter failure,” leaving the Federal Transit Administration to temporarily assume safety monitoring.

Wiedefeld said all Metrorail cables were inspected last year. The cable in Monday’s fire was inspected and passed.

“We have to get out there, saturate the entire system at these 600 locations and do the inspection,” he said.

The work requires inspectors to be close to the third rail and power to the system has to be shut down. If the inspections are done “piecemeal,” Wiedefeld said, the work would take weeks.

After the inspections, there may be a need for additional rail service closings, Wiedefeld said.

“From where I sit, the safety of the public and my employees is paramount,” he said.

Wiedefeld said city bus service will operate normally, but crowding is expected.

Metrorail provides service for more than 700,000 customers a day throughout the Washington area. It’s the second-busiest system in the nation, serving 91 stations in Virginia, Maryland and the District of Columbia, according to its website.

Washington Metropolitan Area Transit Authority was created by an interstate compact in 1967 to finance and operate a transit system in the area of the nation’s capital.

CNN/s John Newsome and Rene Marsh contributed to this report.