A door of a Seoul subway train temporarily went out of order, apparently because of a piece of trash, causing inconvenience for passengers during rush hour on Tuesday, officials said.

One of the doors of a southbound train at Gireum Station on Line 4 failed to close at around 8:20 a.m., forcing more than 500 passengers to get off and take the next train.

The exact cause is unknown but a piece of trash stuck in the door is suspected to have prevented it from closing, officials said.

Subway operator Seoul Metropolitan Rapid Transit Corporation immediately conducted a safety check and resumed operations.

Another train reported a similar problem on Monday at Seokgye Station on Line 6 in northeastern Seoul.

One of the doors of the eastbound train was not closing, forcing about a hundred passengers to get off.

“The door error was allegedly caused by a passenger’s prank. (We) have found an ice cream stick between the doors,” authorities said.

The door error neither affected the arrival schedule of other trains nor caused significant inconveniences as it was late at night and only three stops from the last train station, they added.

By Lee Hyun-jeong (rene@heraldcorp.com)