A festival boat with 20 people aboard capsized at Manazuru port in Kanagawa Prefecture Thursday night after some 30 more people attempted to board it from a wharf, police said Friday.
There were no injuries. Police said all the people involved -- those on board the ship and those who were attempting to board it -- have been accounted for.
Many of those thrown into the sea swam back to the shore by themselves, police said.
The 12-meter boat had been taking part in the Kibune Matsuri, a traditional boat festival dating back to the 17th century.
The festival is held on July 27 and 28 every year and is one of Japan's three top ship festivals, according to town officials. In the Kibune Matsuri, gaily decorated boats parade on the sea, accompanied by festival music.