Image copyright AFP Image caption China's consul-general in Sabah checks her mobile phone in Kota Kinabalu, where the stricken vessel began its journey

Twenty-three Chinese tourists and two crew members have survived after their boat sank in rough seas off eastern Malaysia, officials said.

Shahidan Kassim, a minister in charge of national security, told reporters that six people were still missing,

The catamaran sank on Saturday - the first day of the Chinese New Year holiday.

It sparked a major air and sea search covering 400 nautical square miles.

"We will deploy search assets that can operate at night, and continue our rescue operations to locate those who are still missing," Mr Shahidan told a press conference in Malaysia's eastern state of Sabah.

The catamaran left Kota Kinabalu in Sabah on Saturday at 09:00 local time (01:00 GMT) and was heading towards Pulau Mengalum, a popular tourist island 60km (37 miles) west of the city.

Image caption The boat left Kota Kinabalu en route to the nearby island before it disappeared

Three crew members were on board the vessel, along with 31 passengers.

The Malaysian Maritime Enforcement Agency said it received a distress call from the boat but contact was lost soon after.

The owner of the vessel alerted authorities on Saturday night that it had never reached the island, and the search operation was launched.

The boat's skipper and one of the two surviving crew members were found alive earlier on Sunday off a nearby island, where they had managed to swim to safety. Eighteen of the tourists were found by fishermen, and five others by a tugboat.

Rescue hit by rough seas

"According to the skipper, the boat was 'broken' after being hit by waves and sank," the head of the Malaysian Maritime Enforcement Agency said in a statement.

The head of the Malaysian navy, Ahmad Kamarulzaman Ahmad Badaruddin, said ships and a C130 aircraft were searching for those still missing.

Authorities said the hunt had been hampered by rough seas and strong winds in the search area.

Chinese President Xi Jinping has "demanded all-out search and rescue efforts" by Malaysia, according to China's official Xinhua news agency.

Malaysia's Prime Minister Najib Razak has said he is monitoring developments closely.