An Indonesian hostage held by Islamist militants in the southern Philippines has swum his way to freedom, but another drowned and a Malaysian captive was shot in the back while escaping.

The two Indonesians and the Malaysian separately escaped while Philippine marines were attempting to rescue them on Simusa island in southern Sulu province.

The escapes leave at least three more hostages in the custody of the Abu Sayyaf Islamist militant group, which is blacklisted by the US and the Philippines as a terrorist organisation.

The remaining captives include the Dutch bird watcher Elwold Horn, who was kidnapped by the militants in 2012, and two Filipinos.

One of the Indonesians, Heri Ardiansyah, was plucked from the waters by marines onboard a gunboat while they recovered the body of his companion, Hariadin, who had drowned.

The marines killed three Abu Sayyaf captors who were trying to chase the two Indonesians at sea.

The Malaysian, who was identified by the military as Jari bin Abudullah, was shot by the militants on Thursday while he was running away as marines tried to rescue him and engaged his captors in a gun battle.

Government forces surrounded Simusa island to hunt down the remaining Abu Sayyaf gunmen.

Abudullah was flown to Zamboanga city, where he was in a critical condition in hospital.

The three hostages were kidnapped off the coast of Malaysia’s Sabah state on Borneo island in December last year and taken by speedboat to Sulu, a predominantly Muslim province.

Army troops on Friday clashed with about 80 Abu Sayyaf gunmen in the mountainous ton of Patikul town on Sulu.

Three soldiers and four militants died and several were wounded on both sides.

The rebels belong to an Abu Sayyaf faction led by commander Hajan Sawadjaan and aligned with Islamic State.

Sawadjaan is the main suspect in the deadly bombing of a Catholic cathedral in Sulu’s capital Jolo in January.