(Reuters) - The bodies of four people have been found in Moscow's sewer system and several others are still missing after becoming trapped by heavy rain during a guided tour underground, the TASS state news agency reported on Monday.
Moscow Mayor Sergei Sobyanin called it a "terrible tragedy", without specifying the number of victims. He said the search for missing people was continuing, and investigators were establishing details of what happened.
TASS said authorities had opened a criminal case and the organisers of the tour were being questioned. It described the excursion as illegal. Another agency, RIA, said eight people in total were believed to have taken part.
Heavy rain in Moscow on Sunday caused water levels in the sewage system to rise sharply, preventing the people from escaping to the surface, TASS quoted rescue workers as saying.
The dead included a company employee, his 15-year-old daughter and 17-year-old nephew, social media sites reported. Reuters could not verify the reports.
A number of guides offer tours of Moscow's sprawling sewer system, parts of which date back to the 19th century.
(Writing by Gareth Jones; Editing by Mark Trevelyan)
