All train services between Cardiff and Newport have been suspended due to a 'chemical incident' at the Freightliner depot near the main south Wales railway line at Newland Road near Cardiff.
British Transport Police say that they were called to Wentloog Freightliner Depot at 16:57.
Network Rail says that Ethanol has leaked and there are concerns that it may catch fire or explode. It is not known when services will return to normal.
Buses are replacing rail services, extending journey times by 60 minutes.
A gas container at the depot was overfilled with ethanol, and there are concerns this may lead to the container exploding.
A cordon has been put in place around the depot and the railway line between Cardiff and Newport has been suspended, trains in the surrounding area are therefore likely to be subjected to extensive delays.
Passengers are advised to check with National Rail Enquiries on 08457 48 4950 or www.nationalrail.co.uk to obtain the latest travel advice and information.
Well it's not too bad out there at the moment! Some brighter spells - and perhaps not feeling quite as bitter as it has done of late
Western areas again in line for a damp and drizzly day - the best of the sunshine further inland.
After a relatively mild start to the night, temperatures are tumbling as skies clear. Frost and fog likely inland