Twenty passengers were stuck in a lift at Elephant and Castle tube station when a power cut caused it to break down late on Tuesday night.
People were trapped for more than one hour as they waited for fire crews to come and rescue them.
The two-hour power cut, which also left thousands of homes in the dark and shut other stations, was caused by a fault at an electricity substation.
Commuter Ed Bradshaw criticised Transport For London's chaotic response to help them.
He told the Evening Standard: "Through the intercom we were assured the policy was to call the fire department, who were on their way — however they didn't arrive for over one and a half hours.
"Some elderly staff tried to prise open the doors, without success. Inside, we managed to open the doors enough to jam a fire extinguisher between them and get some air. There was no contingency plan and staff didn't have a clue what to do or what to tell us.
"Goodness knows what they'd have done in a real emergency — for example, if there was a fire. None of the controls behind a metal panel in the lift, which we tried pressing, had any effect on the situation."
"People were left to make alternative arrangements to get home, at almost midnight," he added.
TfL denied any wrong doing and said it followed correct emergency procedures.
Phil Hufton, London Underground's chief operating officer, said staff acted "quickly and professionally", adding: "We apologise to customers affected by this incident, caused by a National Grid power supply problem."