National Rail say the incident happened earlier today, Sunday, December 27.
The incident has led to the closure of some rail lines while the incident was investigated.
Disruption is expected to continue between Shenfield and Southend Victoria until 8pm.
No further information has yet been released about the status of the person hit by the train.
A bus replacement service is currently operating between Billericay and Southend Victoria.
Tickets will be accepted on c2c services between London Fenchurch Street and Southend Central, rail officials say.
A National Rail spokesman said: “If you’ve been affected by what happened on the network today, there is always someone to talk to.
“You can contact the @Samaritans on 116 123 from any phone for a confidential chat.”
We will be bringing you the very latest information when we get it.
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