Thousands of people faced major delays after a train broke down in Kent and passengers on a separate service forced the doors open because of the heat.
Southeastern said the first set of delays were caused when a train halted at Dartford on Monday afternoon.
Commuters told the BBC their journeys had been delayed by about two hours.
Southeastern said Network Rail had to turn the third rail off after passengers walked on the tracks.
A Southeastern spokesman said:
“We do realise it’s very frustrating to be delayed and we’re sorry that people have been – particularly on such a hot day. We do all we can to keep services moving.
“We urge customers not to walk alongside railway lines as this is very dangerous, it inevitably prolongs disruption and makes a difficult situation worse.
“We’d like to say sorry and thank those who were caught up in any delay for their patience this evening.”
People travelling between central London and Gillingham were warned to expect disruption to services.
via BBC News