By Alkis Konstantinidis KOS, Greece, (Reuters) - A passenger ship that is housing Syrian refugees set sail from the Greek island of Kos on Wednesday, heading for the mainland as authorities struggle to cope with a wave of arrivals. The ship, which has acted as a floating accommodation and registration centre since Sunday, was heading for the northern port of Thessaloniki, Greece's second biggest city, where it was expected to arrive on Thursday morning. Local authorities in Thessaloniki were taken by surprise to hear the ship would be heading their way but would hold meetings to handle the issue, the city's deputy mayor for social policy, Kalypso Goula, told Athens News Agency the municipality.