Passengers were left stranded for more than 12 hours without food, water or heating after two South Western Railway trains broke down.
The 17.05 Waterloo to Weymouth and 18.24 Southampton to Poole services both broke down separately on Thursday.
After merging and becoming one service, the train stopped again near to Christchurch where passengers were not released until after 6am on Friday.
One commuter, Paula Baker, sent a desperate video message pleading for help, which was filmed in the dark after the service lost electricity.
She said the driver had locked himself in his cabin, and said nobody had given them any information as to what was happened.
Early on, she said people were playing music and dancing to try to stay warm - but as the night wore on, people got too tired and cold to move or speak much.
Firefighters arrived shortly after 7am to provide them with water, she said. Kerry Collinson said passengers on board a stuck South Western Railway services had been "desperate" for help.
She tweeted: "Train full of passengers stuck with NO power outside new Milton for several hrs. No heating good drink or WCs....No help from train operators ...7 hrs now and desperate please help them."
A spokesman for South Western Railway apologised.
Passengers should not attempt to travel today, he added.
He said those who had already started their journey should return as soon as possible, as the train service would be closing early.