Hopes are fading for more than 80 people still missing after a Tanzanian ferry sank near Zanzibar's main island. At least 63 people are known to have died in the disaster and about 145 have been rescued. The MV Skagit ferry had left the city of Dar es Salaam on mainland Tanzania on Wednesday with 290 people on board. Survivors have told the BBC that the crew gave them no instructions on how to evacuate and merely told them to calm down. They say there was only one exit and that many people were trapped and went down with the ship when it sank off Chumbe island. Some passengers have told how they jumped overboard, clinging to life-boats that automatically inflated, until they were rescued by a tug. A naval search operation resumed at first light, but was being hampered by bad weather. "Search operations continue but it is now almost impossible survivors will be found," Zanzibar police spokesman Mohamed Mhina told reporters. "The weather was very bad, there were big waves and strong wind." Tanzanian President Jakaya Kikwete said in a statement: "This tragedy affects all of us, and the pain and suffering of those affected is the pain and suffering that we feel." Tatu Kwiyela, 35, from mainland Tanzania, survived the sinking but lost her nine-month-old son. "I was swept away by strong waves," she told the Reuters news agency. "I tried to hang on to him but he disappeared into the sea." Ali Mohamed Shein, president of the semi-autonomous archipelago of Zanzibar, has declared three days of national mourning. The ferry left Dar es Salaam at 12:00 local time (09:00 GMT) on Wednesday bound for the main island of the Zanzibar archipelago. Hamza Kabelwa, director of the Tanzania Meteorological Agency, told the BBC's Swahili service that a warning had been issued for vessels not to make the crossing because of the rough seas. Zanzibar's transport minister told reporters that two Europeans were among the dead. Police said more than 10 other foreign tourists - including a group of Dutch holidaymakers - had been rescued. The BBC's Hassan Mhelela in Dar es Salaam said on Thursday morning there were many anxious relatives of missing MV Skagit passengers at the airport waiting to fly to Zanzibar. The route between Dar es Salaam and Zanzibar is a busy crossing, popular with both Tanzanians and foreign tourists. Last September, nearly 200 people died when an overcrowded boat with 800 people aboard sank off Zanzibar.