Indonesian authorities sank at least eight boats on Monday to commemorate the country's national day as the biggest southeast Asian nation cracks down on illegal fishing.

Eight illegal fishing vessels from the Philippines were destroyed on the choppy seas off of the North Maluku province and North Sulawesi province. Both areas are well-known for their marine resources.

Illegal fishing costs the vast archipelagic nation around $25 billion a year, officials said.

The country has vowed to tackle the illegal activity with hardline action and has blown up over 20 foreign fishing vessels caught in Indonesia since 2014.

Earlier this year, Indonesia and the United States announced a partnership program to improve marine law enforcement and cut down illegal fishing.

In 2016, there have been a number of clashes between Indonesian naval vessels and Chinese fishing boats in the Natuna Islands.

The operation, which is being carried out across the country, is expected to destroy 71 vessels by Wednesday (August 17), when Indonesia celebrate its 71st independence day.

Instead of blowing the boats up, authorities sunk the vessels by making holes in them, as police said bombing the boats damaged the environment.