Service on Metro’s Red Line was disrupted Saturday night in much of Northwest Washington and Bethesda due to a fire near the Friendship Heights station. At least one train was evacuated after smoke filled the tunnel. No injuries were reported.

About 8:45 p.m. Metro said it had begun to send trains through the affected area on a single track, although Metro’s website continued to say service was suspended.

By late Saturday, full details of what had happened remained unclear.

An official Tweet from Metro described a “smoke incident,” and said it was “possibly the result of electrical arcing near Friendship Heights.”

The official Metrorail Info feed said track inspections were under way about 10 p.m.

It said that the “root cause has not yet been determined.”

That left uncertain whether the reference was to what had caused the problem with an insulator, or whether some different problem entirely was involved.

However, most accounts described smoke, whatever the cause.

In a Twitter post, someone describing himself as a passenger on a train involved in the incident called it “one of the scariest moments of my life” and said “communication was horrendous.”

Another person claiming to be a passenger said the train stopped suddenly, and chaos erupted. “People start jumping over the seats, shoving, yelling, cursing.” Reportedly the passenger detected the kind of smell produced in an electrical fire.

Still another passenger described a thin haze of smoke in her northbound train while it was on its way from Tenleytown to Friendship Heights. She said she could smell smoke in the fourth car of the trrain

“Everyone was pretty calm,” she said, but acknowledged that she was frightened. The train eventually moved back to Tenleytown.

The D.C. Fire and EMS Department said heavy smoke was reported at the Friendship Heights station about 7:15 p.m.

The smoke, according to the fire department, was “centered around” an insulator on fire at the platform. Insulators prevent current from leaking from the third rail, which carries the electricity that powers the trains. Dirt, moisture or structural damage to the insulators can degrade their capacity to block the flow of current. As electricity begans to push through the insulator it produces heat, smoke and sometimes fire in what is described as arcing.

Arcing insulators have been a significant problem for the system.

Earlier Saturday, an arcing insulator was reported near the Bethesda station. Trains single tracked in that area for a time.

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