Passengers were stuck on trains for hours after a serious incident shut major routes into and out of London.
Frustrated travellers told on social media how they were held on trains while many others were left waiting at stations in the early hours of Friday morning.
There were unconfirmed claims that a driver was injured in the incident, though there was no official explanation.
London Euston tweeted before services resumed: "All lines are still blocked due to an incident at #HarrowandWealdstone. Emergency services are on site so we can’t reopen until everyone is safely off the railway.
Were you affected by the incident? Email webnews@mirror.co.uk.
"We’re sorry to those of you caught up in the disruption. We’re doing our best to get you moving."
National Rail also said that lines were blocked between London Euston and Watford Junction as emergency services dealt with an incident.
It stated: "The emergency services are dealing with an incident between Wembley Central and Watford Junction. To allow them to work safely, all lines are blocked.
"Trains between London Euston and Watford Junction may be cancelled or delayed.
"Major disruption is expected until the end of service."
One person tweeted: "My 10pm train left Euston, got stuck in an 'incident' at Harrow and got sent back to Euston. Been on it for 3hrs now and am 0 miles closer to home."
Another traveller wrote: "00.20 Stuck at Euston Station on a train since 10.30pm.
"No idea when we are leaving Euston or when I will get home. Emergency services are dealing with a serious incident at Harrow and Wealdstone. My thoughts and best wishes are with all those involved."
One person at Euston claimed that a train driver had been injured in an incident.
He tweeted: "Coming into to Euston, our announcer has just said emergency services still working as the driver was also seriously injured!"
The trains affected have been Avanti West Coast between London Euston and Glasgow Central/Edinburgh/Liverpool Lime Street/Manchester Piccadilly/Wolverhampton.
As well as London Northwestern Railway between London Euston and Birmingham New Street/Milton Keynes Central/Northampton.
And London Overground between London Euston and Watford Junction.
One Avanti West Coast traveller tweeted: "I understand there’s been an incident on the line.
"We’ve been at Euston for nearly 2 hours and unable to move. Surely if trains or transport is still unconfirmed you should be helping your passengers get home to their destinations?"
Shortly after 4am National Rail tweeted to say that services were returning to normal.
It said: "CLEARED: Trains between London Euston and #WatfordJunction are now able to run normally following the emergency services dealing with an incident between Wembley Central and Watford Junction."
