Four vessels, an An-74 plane and two helicopters are involved in search and rescue efforts on Monday after an oil rig overturned in the Sea of Okhotsk in Russia\'s Far East. The Kolskaya drilling rig with 67 people aboard was being towed in a severe storm, when it overturned and sank some 200 km (125 miles) off Russia\'s Sakhalin Island early on Sunday. Of 67 people onboard, 14 were rescued, four were found dead and others are missing. The An-74 plane found two life rafts on Monday morning, but it is yet unknown whether there were any survivors in them. A lifeboat was found earlier on Monday, but it was empty. On Sunday, four empty life rafts were found. Captains of fishing and trade vessels in the vicinity of the accident area were also ordered to take part in the search-and-rescue operation. The weather forecast for the search zone is currently being verified, but the rescue operation was hampered on Sunday with strong winds and waves of 4-5 meters. An investigation was launched and survivors will be questioned later in the day. Violations of safety rules and unfavorable weather conditions are seen as the most likely causes of the accident. \"The investigators on Monday will question three crew members who are currently in the central regional hospital in the town of Nogliki in Sakhalin. The remaining nine survivors and crew of the Neftegaz-55 tugboat which transported the rig will be questioned upon their arrival to the port of Korsakovo,\" a spokesman for the regional investigation department said. The Kommersant business daily said on Monday that about a half of all people onboard the oil rig were not authorized to be there under the transportation rules. \"Approximately a half of all people onboard - drill rig engineers, their assistants, crane operators and so on - had no relation to the transportation of Kolskaya,\" an unnamed source close to the investigation told the newspaper. Under the rules, only the captain and a minimal part of the crew needed for the transportation process are allowed to stay onboard when the rig is tugged. It is forbidden to tug a drilling rig with passengers onboard. The drilling rig, built in 1985 in Finland, carried out work under a contract with energy giant Gazprom. It can take up to 102 people on board, was. The rig, which is 69 meters long and 80 meters wide, was intended to drill a well at a depth of 3,500 meters.