Southern Rail services may be delayed or cancelled after a vehicle struck a bridge near Hove, according to Southern.
A police spokesman said reports of a lorry hitting the bridge were received at 10.29am.
The lorry is currently stuck under the bridge in Fonthill Road, Hove.
Trains are reportedly at a stand at Worthing station with no services running towards Brighton.
Services elsewhere in the county are subject to ‘major disruption’, according to Southern.
Sussex Police have handed the matter over to British Transport Police.
Network Rail said services were temporarily stopped but have now resumed. Some services are expected to be delayed.