Trains through Ilford, Seven Kings, Goodmayes and Chadwell Heath have been delayed and cancelled this morning because of the heat.
Temporary speed restrictions have been put on the line from Liverpool Street to Shenfield as a precaution because the metal rails have reached abnormally high temperatures.
A Network Rail spokesman said the track can heat up to over 50C - 20C higher than air temperature - in prolonged spells of good weather and trains are slowed down to prevent any damage.
Greater Anglia cancelled services as the measures caused trains to slow down and disruption could continue until the temperature falls.
The speed restrictions are in force until further notice.
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