Passengers on a southbound subway leaving King station during the busy Thursday morning commute were startled when the train doors opened inadvertently — the second such incident in less than a week.

The incident happened around 8:30 a.m. as the train was leaving the station. TTC spokesman Brad Ross said the train had received a red signal and stopped. That’s when a trainee operator, who was accompanied by an instructor, accidentally opened the doors.

“At the end of the day it is quite a monotonous job but it is a safety critical job so my message to my guards, my operators: please do maintain concentration,” TTC CEO Andy Byford said. “This is something that we absolutely have to get right.”

Power was cut and the train was taken out of service at Union station. The situation led to a nine-minute delay.

Haley Greenberg was on the train at the time. She claims the subway was moving when the doors opened.

“In the future, I will be far away from the doors,” she said.

This latest incident comes just days after Byford issued an apology for a series of delays during Monday evening’s commute. On Monday night, the doors of a train stopped north of Dupont station inadvertently opened to the surprise of riders.

TTC chair Karen Stintz told CityNews that door opening was also due to human error.

Human error may not be a problem much longer. The TTC is installing a sensor system that will only allow the doors to open on the platform, unless there’s an emergency.

“We are moving to an automatic train control system over the next couple of years, on the Yonge line initially,” Byford said.

The TTC expects it to be up and running by 2017.

Last month, the TTC unveiled its first-ever customer charter, promising better communication with riders and increased punctuality, cleanliness and customer service.

Doors opened on a moving train for the 2nd time this week? #ttc get your act together.Do you want someone to fall out? @ttchelps — Prat (@P_Rat) March 21, 2013