UPDATE -- Mystery smoke kills 1, injures scores in DC metro... 'People were throwing up around me'... Terrified Passengers Stuck On Train...

(NBC Washington) -- One woman is dead, dozens of other people were hospitalized, and three remain in critical condition after the upper level of the L'Enfant Plaza Metro station in southeast D.C. filled with smoke Monday afternoon.

A Virginia-bound Yellow Line train was in the tunnel just south of the station around 3:20 p.m. when it stopped for unknown reasons.

Dozens of people were trapped inside the train's cars as the tunnel filled with thick, black smoke.

"People could barely breathe," passenger Denzel Hatch said. "They had to evacuate us through the tunnel and walk back through the front. No electricity, no visibility, nothing. Couldn't see anything at first."

"You're hearing other people crying, you're seeing people passing out... it was a horrific thing to witness," passenger Adjoa Adofo said.

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