After changing trains mid-track, passengers finally arrived Paris more than 24 hours late.
SNCF said the cause was broken overhead lines, or catenaries, over a 60km stretch.
"We had a series of exceptional events," said Jean-Luc Gary, local Nouvelle-Aquitaine head of SNCF Réseau, which operates the tracks. "Our first thoughts to go to the passengers. An inquiry has is underway."
Two other trains that left Hendaye experienced huge delays with passengers finally wheeled back to their departure station overnight then driven to Bordeaux.
Furious passengers denounced the "appalling" handling of the incidents by SNCF, which has pledged refunds three times the original price of the ticket by way of compensation.
"We are in a train that left Biarritz at 12.30pm and it's now 3am. 1,100 passengers on board: could we have masks so as not to add France's biggest cluster to the other records of this nightmarish train ride?," asked one passenger on Twitter.
"SNCF has left us like dogs," said a second.
Another showed a picture of his two-year old son asleep on the floor "mid-Covid".
Marjolaine, a stricken passenger from another stricken train, said: "It was hell: no more bog roll, no grub, only a tiny bottle of water. It was hot with masks on and they forced us to stay on board when we could have got out."
"We didn't know whether we'd die first from hunger, thirst, Covid or hygiene," she told France Info.
Some kept their sense of humour, with one passenger noting: "What I regret most is not seeing my children grow up."