KUALA LUMPUR, May 4 -- Four people, including a Chinese citizens and two Spanish, remained missing at sea in Malaysia's Sabah state, police said Wednesday.

The four people were travelling in a speed boat in Sabah's Kudat area on Monday evening but failed to arrive at the destination, according to the police.

Search and rescue operations were launched after the authorities received reports on Tuesday.

Police said the cause of the incident had yet to be determined, adding that the area had waves of 0.5 to 1 meter at the time of the incident.

China's Consulate-General in Kota Kinabalu, the state capital, confirmed to Xinhua that the missing Chinese citizen was from China's Hong Kong Special Administrative Region, who was operating a vacation resort in Sabah.

A Consulate-General official said they had informed the family of the missing Hong Kong citizen, and they have also been in close contact with the local authorities, urging for greater efforts for search and rescue.

Helicopters and plane were dispatched but the missing have yet to be found.

The state of Sabah on North Borneo attracts many tourists from around the world for its beautiful beaches and rainforests. The Malaysian authorities have strengthened security in recent years following threat posed by militants operating in the neighboring southern Philippines.