Commuters have complained of overcrowded carriages on South Western Railway (SWR) services on the second day of a five-day strike.
Some passengers have described the situation as “disgusting” and “shambolic”, with one woman reportedly fainting due to “overheating”.
Members of the Rail, Maritime and Transport union (RMT) have walked out over the role of train guards.
SWR has apologised for “continued disruption” to its services.
The operator, which runs services in London and Berkshire, Surrey, Hampshire, Dorset, Devon, the Isle of Wight and Somerset, previously said a reduced service was running across the network and described the action as “unnecessary”.
Passengers have been venting their anger on social media.
One tweeted: “The heat on the non air-conditioned trains is unbearable. Packed in so tight it would be against livestock’s animal rights to endure.”
Another user has been tweeting throughout his journey and described how a woman “collapsed” because she “overheated”.
“Physically not being able to get on a train at Surbiton because the #SWRStrike is absolutely disgusting – I left almost 2 hours before I needed to and I’m STILL not going to make it to my very important meeting,” added another.
A South Western Railway spokesman said: “Despite this action, services, including the additional ones we’ve added today, are very busy but running well with our team of contingency guards and rostered guards that have reported for work.
“We would still urge people to travel outside of the peak periods wherever possible and if they feel unwell, seek assistance from platform staff or station Help Points rather than board a train.”
RMT has not yet responded to a BBC request for comment.
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