British Prime Minister Boris Johnson said he was saddened to learn of the "very serious incident" and his thoughts were with all those affected.
The train appeared to have been carrying very few passengers.
The government has been advising Britons to avoid public transport wherever possible as part of efforts to reduce transmission of the coronavirus.
Read also: Jakarta Extends Partial Lockdown Yet Again to Curb Covid-19 Spread
Britain has one of Europe's lowest rates of fatal rail accidents, with a stronger safety record than Germany or France in recent years, according to Eurostat data that includes unauthorized people on railway tracks and at level crossings.
For passengers, European railways are very safe, with just 13 rail passenger deaths across the European Union's 28 member states in 2018, according to the most recent available data from Eurostat. One of those was in Britain.
The worst rail disasters in Britain in recent decades were a 1999 collision between two trains at Ladbroke Grove, in London, in which 31 people died, and a 2001 accident near Selby in Yorkshire, northeast England, in which 10 people died after a car ran onto the track and was hit by two trains.
(Writer: Estelle Shirbon | Editors: Philippa Fletcher, Jonathan Oatis, Gareth Jones)
Simak breaking news dan berita pilihan kami langsung di ponselmu. Pilih saluran andalanmu akses berita Kompas.com WhatsApp Channel : https://www.whatsapp.com/channel/0029VaFPbedBPzjZrk13HO3D. Pastikan kamu sudah install aplikasi WhatsApp ya.