Houses have been evacuated and trains stopped because of the risk of a gas cylinder exploding after a shed fire.
The acetylene cylinder was in an industrial shed at a car dealer's yard on Vale Road, Northfleet, Kent.
Fire crews were called just after 1300 BST on Sunday, and were cooling down the cylinder after spending more than two hours tackling the blaze.
A 200m radius was cleared and South Eastern Trains services are affected into London Charing Cross and Victoria.
A Network Rail spokesman said there was a "small possibility" the nearby section of track between Gravesend and Dartford could be shut in both directions for up to 24 hours.
"Hopefully it will be up and running again for commuter services in the morning," he added.
Services suspended
Network Rail is getting updates on the situation from Kent Fire and Rescue at regular intervals.
Gravesend to Charing Cross services are starting and finishing at Dartford and replacement buses are running between Dartford and Gravesend.
Gillingham to Charing Cross trains are suspended in both directions and a shuttle service is operating between Gillingham and Gravesend.