People were stranded in overcrowded and overheated trains on line four of the capital's metro for two hours after a signalling issue.

It has prompted the Autonomous Parisian Transportation Administration (RATP) to launch an internal investigation.

There were five trains stuck from around 6pm onwards before a woman got her bag stuck in a door at the Cité station that triggered an alarm and meant some trains were unable to restart due to technical problems.

Later on, the entirety of line 13 was stuck from 8.30pm CEST for 90 minutes due to a computer failure, while a broken-down train in Seine-Saint-Denis also disrupted traffic on the B and D route of the RER.

Around 125 RATP workers were deployed to manage the line four incident, with passenger evacuations starting 40 minutes earlier.

"This is an exceptional incident because it is an accumulation of incidents that took place in a very short period of time," said RATP rail network director Agnès Ogier, as reported by 20 Minutes.

Paris' fire department also sent six emergency vehicles to Montparnasse, Saint-Germain-des-Près and Saint-Placide stations to facilitate the evacuation.

Paris is home to one of the oldest urban transit systems in the world but with that comes increasing complaints of overcapacity and outdated infrastructure by users. 

More than 10 million visitors are expected in Paris next year for the Games which begin on July 26.

As a result, attempts are being made to expand the travel options in the city, with 37 new metro trains ordered at a cost of €1 billion (£860 million/$1 billion), which will double the number in circulation.

RATP has also launched a recruitment plan for the Games as it aims to hire more than 6,600 new employees with 4,900 of those on permanent contracts.