The search for a boat with four people on board missing since Monday in the waters of Pulau Balambangan, Kudat, has been extended to cover 3,600 sq nautical miles.

Malaysia Maritime Enforcement Agency Sabah and Labuan Region director First Admiral Mohd Zubil Mat Som said a study of the winds and currents indicated that the boat could have drifted west or northwest.

The aerial and sea search was being conducted by Maritime Malaysia, the Royal Malaysian Navy and Royal Malaysian Air Force, he said in a statement.

The boat carrying the four people - Spanish nationals David Hernandes Gasulla, 29, and Martha Miguel, 30, Chinese national Tommy Lam Lai Yin, 44, and a Malaysian woman identified only as Ella, 23 - did not arrive at Tanjung Simpang Mengayau as scheduled after having left Kampung Batu Sirih, Pulau Balambangan, at about 5.30pm last Monday.