The doors on the left side of the train were reportedly open for close to a minute and 25 seconds as it traveled from Arjangarh to Ghitorni near Delhi's border with Haryana, at around 9:40 am.
The incident took place on the Yellow Line that operates from Jahangirpuri to Huda City Centre stations.
In a statement, the Delhi Metro Rail Corporation said it appeared to be "an error by the train operator and he has been suspended with immediate effect."
The news set the social media abuzz. Among the many comments on Twitter, one read, "Delhi metro wanted to give mumbai local feel to its commuters".
Delhi Metro ferries about 23 lakh passengers every day.
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