Investigations into two train derailments in the United Kingdom in two days "will look at all possible causes and factors," a boss for the rail company Network Rail said, adding the hot weather had "presented exceptional challenges to the railway."
It comes after a second train derailed less than 24 hours after two passengers were seriously injured when a service operated by Southern Rail came off the tracks in East Sussex.
A train derailed at 2:12 pm (1312 GMT) on Friday south of Wickford railway station in Essex, British Transport Police said.
BTP said officers, paramedics and firefighters are at the scene after reports that the rear carriages of the train have derailed in an upright position.
No injuries have currently been reported.
Martin Frobisher, group safety and engineering director at Network Rail, said: "We are currently responding to a derailment incident near Wickford station in Essex, and we are working quickly to understand the situation and to provide assistance where needed. Two carriages have derailed but remained fully upright, and there are no significant injuries reported."
"We will also conduct our own internal investigations, in which we will look at all possible causes and factors."
"The unprecedented hot and dry weather that we have experienced this summer has presented exceptional challenges to the railway."
"In response, we have taken several additional proactive steps to manage and mitigate the impact on the railway, including closely monitoring the temperature of tracks, implementing speed restrictions where it is appropriate to do so, and planning track renewals around high temperatures."
"Our continued focus remains on supporting those affected by these incidents, working at pace to understand the causes, and doing all we can to get services back running safely as quickly as possible."
A major incident was declared by BTP in East Sussex when three carriages of a train ended up on their side, trapping passengers near the southern town of Lewes on Thursday afternoon.
Around 150 people had been on board the service from London to Eastbourne.
Two people were taken to major trauma centres with "severe" injuries and BTP said on Friday these were not deemed to be life-threatening.
A statement said: "They both remain in hospital and the 18 people who were also treated at hospital for less serious injuries have been discharged."
