The German Shepherd, named Devin, was spotted by police but evaded their clutches and is believed to still be on the run after getting on the tracks by East Finchley at roughly 11.20am on Thursday.
The freewheeling canine is believed to have run in the direction of Mill Hill.
Luca Comencini, 50, was on his way to Camden to give a guitar lesson but got stuck on the tube for nearly an hour.
He told the Standard: “The train came into East Finchley very slowly.
“We waited a few minutes then the driver told us she would proceed cautiously, but didn’t tell us why.
“Then she told us there was a dog stuck under the train.
“After about 20 minutes she started walking through the carriages trying to explain things to us. I asked her twice if the dog was under the train and if he was alive and she said ‘yes’, but she had to wait for colleagues to get on the train and help.
“People were getting very nervous, they couldn’t understand why she didn’t stop the train at East Finchley.”
He said passengers started to doubt the official explanation of a dog on the track was true because they couldn’t see or hear the startled canine.
He added: “Eventually she came back to my carriage with a colleague, they lifted a hatch, did something, and then told us the train would leave in a few minutes. She said it would stop at Highgate where there would be water and help for people that didn’t feel well.
“We got to Highgate almost straight away.”
And here’s a hastily taken snap of Devin. If you see him near Mill Hill do pass it on - meanwhile, Northern line returning to normal. If I hear more - will update here. pic.twitter.com/zAbtrRgxaG
— David Sillito BBC (@DavidSillitoBBC) August 24, 2023
A British Transport Police spokeswoman said: “Officers were called to East Finchley underground station at 11.22am today, following reports of a dog on the tracks.
“Officers have attended and the dog was spotted, the dog is now believed to have left the tracks but is still in the area.”
BBC media reporter David Sillito posted about the chaos.
He said: “In case anyone’s wondering why the Northern Line is suspended at East Finchley. An Alsatian is on the track.
“He was last seen looking very healthy and in good spirits. Just heading in to a tunnel.”
More to follow.