Ten crew members jumped into the sea moments before a tugboat capsized and sank during a salvage operation off Botolan in the Philippines' Zambales province on Monday.

Footage released on Monday shows MTUG SL SUAL 1 listing sharply to starboard as crew members leap into the water and swim before the vessel disappears beneath rough seas.

All 10 were rescued in good condition. The Philippine Coast Guard said strong waves may have worsened the tugboat's list, while investigators are also checking whether it struck submerged metal debris.

The vessel sank in around 24 metres of water with about 15,000 litres of diesel on board. Its fuel tank was initially found intact, while Coast Guard teams patrolled the shoreline and prepared oil-spill equipment as a precaution.

SL SUAL 1 had been deliberately grounded on August 14 after a hull breach flooded its engine room. Nine crew members were rescued at the time, and no oil spill was detected.