Hundreds of trains have been cancelled and others delayed due to 'exceptionally' hot weather today.
Greater Anglia is advising customers not to travel unless "absolutely necessary" on Thursday, July 25.
It said Network Rail had imposed a 60mph speed restriction across the company's entire network, leaving it unable to operate its normal timetable.
As of 10.30am at least 245 trains had been cancelled, according to the Greater Anglia website, and dozens more delayed.
A spokesman for Greater Anglia said: "This is to prevent tracks buckling in the exceptional heat, which would cause much worse disruption as trains would not be able to travel on the damaged section."
It comes as Norwich-based forecaster Weatherquest warned that the mercury could hit 38C across parts of East Anglia this afternoon.
The Met Office, meanwhile, said today is forecast to be "exceptionally" hot.
Greater Anglia confirmed it had cancelled five of its Norwich in 90 services.
It said all tickets dated for July 25 will be valid on July 26.
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