Indonesian relief officials on Wednesday continued the search for several people still missing after a ferry sank on Tuesday in rough seas off the coast of Bali.

Officials say the KMP Yunicee ferry, with 57 people on board, sank shortly after leaving the port of Ketapang on the island of Java for the port of Gilimanuk in Bali, at the western end of the island.

Port Authority official Benyamin Ginting told Agence France-Presse that two ships arrived at the scene shortly after the ferry ran aground and saved around 40 people. But he said many passengers were still trapped as the ferry continued to sink. Many of those recovered were unconscious after hours of drifting through rough waters.

Rescue officials said search and rescue efforts were hampered by rough seas and poor visibility. Seven bodies were eventually found.

Rescue officers displayed life vests and other materials recovered from the ferry during search and rescue operations. Ginting said some of the life jackets had been locked so that they could not be worn.

No cause of the sinking has been identified. Ferry tragedies are common in Indonesia, an archipelago of more than 17,000 islands, often to be blamed for poor enforcement of safety regulations.