BUENOS AIRES (Reuters) - An intercity train in Argentina has derailed near the eastern town of Olavarría, injuring at least 21 people, local authorities said on Tuesday.

       Video images showed the passenger train with many carriages off the rails, some turned over on their sides, in the middle of fields in a rural area of the South American country.

       "At the moment, 21 passengers have received treatment at the hospital," Olavarría mayor Ezequiel Galli wrote on Twitter, adding that five were children who had now been discharged and that a 40-year-old passenger had suffered a cranial injury.

       He said all those hurt had minor injuries and were being taken care of.

       "The rest of the passengers are being transferred to the Olavarría Municipal Exhibition Center (CEMO) where they will receive appropriate attention until they can restart their trip," Galli added.

       Trenes Argentinos, the state-owned company that operates the country's train network, confirmed the accident in a statement on Twitter, saying the causes were not yet known and were still under investigation.

       The 333 train connects the capital city of Buenos Aires with the port city of Bahía Blanca.

       (Reporting by Agusting Geist; Writing by Adam Jourdan, editing by Ed Osmond)