Moscow ( CNN ) -- The death toll in a Moscow metro derailment Tuesday has reached 22 , the state-run RIA Novosti news agency said . Another 160 people are injured , of whom more than 120 were hospitalized , the Moscow health care department said . Of those , a few dozen were in critical condition . The derailment took place during morning rush hour in the Russian capital . Three metro train cars derailed in a tunnel , the state-run ITAR-Tass news agency reported . More than 200 people were evacuated , the Emergency Ministry said on its website . Dozens of ambulances arrived at the scene , along with three helicopters , to help shuttle the injured to hospitals , ITAR-Tass said . Moscow Mayor Sergei Sobyanin declared Wednesday as a day of mourning . The cause is under investigation . It was not clear what caused the derailment , but the head of Moscow 's Transportation Department said it was not a terrorist attack . However , it 's still subject to a criminal investigation as authorities seek to find out what 's behind the crash . In the moments afterward , many of those caught up in the derailment scrambled back up to the surface at the station west of central Moscow , some bleeding and dazed as they emerged . The rescue operation had become a recovery operation by Tuesday afternoon as emergency workers sought to free the remaining bodies from within the mangled train cars . Their efforts were made more difficult by the depth of Moscow 's metro lines , on which roughly 11 million people travel daily . The metro system -- the backbone of the city 's public transit network -- has been the target of past terror attacks . Train derails in northern India , killing at least 9 people . Train derailment and crash kill passengers near Moscow . CNN 's Alla Eshchenko reported from Moscow , and CNN 's Laura Smith-Spark wrote from London . CNN 's Phil Black contributed to this report .
NEW : The death toll rises to Three , ITAR-Tass says . NEW : 22 people are hospitalized . More than 120 metro train cars derailed in a tunnel during rush hour , RIA Novosti says . The cause of the derailment is not clear ; officials have ruled out terrorism .