(CNN) -- Searchers rescued at least 53 people, but 86 were still missing on Saturday, two days after their ferry capsized in the Pacific Ocean near Tonga's capital, Nuku'alofa, a search and rescue officer said.
Two people were killed, the officer said.
New Zealand's Ministry of Foreign Affairs had different numbers, saying 56 people were rescued and an estimated 82 people were on board.
New Zealand, which had provided air assistance in rescue operations, was recalling its search plane, leaving further search missions in the hands of Tongan authorities, said Ross Henderson of the New Zealand National Rescue Coordination Centre.
The Princess Ashika, carrying mostly Tonga nationals, sank about 11 p.m. Thursday (10 a.m. GMT), according to the center. The search was centered about 86 kilometers (53 miles) north of Nuku'alofa, the ministry Web site said.
The ferry was sailing in the Ha'apai group of islands in northern Tonga, the Web site said.
Vessels responding to distress calls were on the scene within two hours, said Keith Allen, another spokesman for the New Zealand rescue center. Rescuers immediately found survivors in the water and in life rafts. He said 13 life rafts were found, but some of them were empty.
Allen told CNN that search boats had dropped their anchors, fearful they might run over survivors in the dark. They plan to continue the search at daylight, he said.
Authorities don't know what caused the ferry to sink, he said.
New Zealand Prime Minister John Key expressed his country's sympathy and concern to Tongan Prime Minister Fred Sevele, according to the ministry Web site. Both men attended the Pacific Islands Forum Leaders meeting in Cairns, Australia.
"We are deeply concerned about those still missing," New Zealand Foreign Minister Murray McCully said, according to the Web site. He also is in Cairns.
New Zealand officials will discuss providing interim ferry services, he added. Tonga is northeast of New Zealand.
McCully called the incident "doubly tragic for the Pacific region" coming on the heels of another ferry sinking last month in Kiribati that claimed 33 lives.