Passenger Ann-Margaret Campbell captured this picture in the tunnel

Up to 100 passengers had to walk about half a mile through a subway tunnel linking Govan to Partick station after the breakdown at 0845 GMT.

Strathclyde Partnership for Transport (SPT) blamed an engineering problem which caused an electrical fault, leaving the train without power.

A spokesman apologised to passengers for any distress and said the evacuation may have been unpleasant.

SPT said the normal procedure is to try and restore power, but this failed.

The electrical fault created fumes and smoke.

It took about 10 minutes to escort passengers to Partick station.

Normal service was restored on the Outer Circle at 1000 GMT.

Bob Wylie, communications director of SPT, said: "We have to apologise to the people who were on the train for any distress or inconvenience this caused.

A few people were upset, one woman was crying and there were schoolchildren on board David Hewitson Train passenger

"The necessary emergency procedures were put into action by subway staff.

"Understandably, some people may have found walking through the tunnel an unpleasant experience."

David Hewitson, 29, a media manager from Glasgow, was on the train.

He said: "The train just stopped suddenly and they told us we would have to walk up the tunnel.

"A few people were upset, one woman was crying and there were schoolchildren on board.

"There was a toxic smell.

"But it was orderly and we were moved to the front of the train and into the tunnel while passengers reassured the woman.