At least 16 people have been killed and dozens more injured after two trains collided head-on outside the city of Larissa in central Greece. The fire brigade said the crash happened between a passenger train travelling from Athens to the northern city of Thessaloniki, and a cargo train from Thessaloniki to Larissa. Konstantinos Agorastos, the governor of the Thessaly region, said the crash was "very serious" and that emergency services were working to rescue people from the train carriages. The cause of the crash is not yet known, but investigations are underway. Greece's Prime Minister Kyriakos Mitsotakis has expressed his condolences to the families of those killed, and said the government was doing everything it could to help those affected. The tragedy has shocked the nation, with many people taking to social media to express their grief and outrage. The Greek Railway Workers' Union has called for an investigation into the cause of the crash, and has urged the government to take steps to ensure that such a tragedy does not happen again.