Passengers board a Metro train in October 2010 at Metro Center station. (SUSAN BIDDLE/FOR THE WASHINGTON POST)

Doors on two Metrorail cars opened without warning Tuesday morning while the Red Line train full of passengers was traveling between stations.

The incident, which transit officials described as “rare,” happened about 9 a.m. on a Shady Grove-bound train between the Van Ness and Tenleytown-American University stations. A passenger aboard the train took a photo of it, and the image was posted to unsuckdcmetro, a blog that is a sounding board for critics of the Metro system.

Metro chief spokesman Dan Stessel said no injuries were reported. He said the train operator called Metro’s command center and car maintenance personnel were sent to meet the train at the Tenleytown-AU stop. The train was unloaded and taken to a rail yard for “diagnostic testing,” he said.

Stessel said incidents in which doors open on moving trains are “extremely, extremely rare.” He said it had been “multiple years” since a similar incident.

The two rail cars are part of Metro’s 1000 series, which were involved in a deadly crash in 2009 on the Red Line and are expected to be replaced soon, based on a recommendation from the National Transportation Safety Board.

Metro has had chronic problems with doors on rail cars. About two-thirds of train delays involve trouble with doors, Metro officials recently told board members.

The Tri-State Oversight Committee, which helps to oversee safety at Metro, said that Metro reported the incident and that the committee plans to send some of its personnel to help look at the rail cars in the next day or two.

“As rail transit hazards go, this is very significant,” said Matt Bassett, head of the Tri-State Oversight Committee. He said Metro’s 4000 series rail cars had reports of doors opening unexpectedly in July 2010 and Metro grounded the 4000 series fleet.

Stessel said the 4000 series problem was a “systemic issue” and the cars were removed from service at the time. Metro officials and Bassett said the problem was fixed.

There has not been a similar systemic problem identified in the 1000 series, Stessel said.