Commuters are facing delays of up to 30 minutes after the Brighton to London mainline became blocked.
Network Rail said the delay between Gatwick and East Croydon was due to an obstruction near Coulsdon, near Croydon.
It happened this morning and was still blocked at 8am.
Train operators said delays will continue until further notice.
First Capital Connect is accepting Southern passengers between London and Brighton.
For more details visit www.nationalrail.co.uk/service_disruptions/today.html, call 0871 200 49 50 or see Twitter hashtag: #Coulsdon.
See the latest news headlines from The Argus:
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here