A Chinese ship has been detained in the Galapagos Islands after it was caught carrying 300 tonnes of endangered sharks.

National park rangers said they "alerted" the Ecuadorian Navy, which has jurisdiction over the islands, that Chinese refrigerator ship Fu Yuan Yu Leng 999, was 34.5 nautical miles off the island of San Cristóbal.

The Navy and other authorities boarded the vessel and found 300 tons of frozen sharks, including hammerhead sharks as well as other endangered species, said national park director Walter Bustos.

The ship is being investigated on suspicion of poaching and causing environmental damage.

The Chinese ship carried a 20-strong crew who could face up to three years in prison for a crime against protected marine wildlife.

Bustos added the ship was "the largest vessel" that had been caught in the national park area, which covers over 51,000 square miles, making it the second largest protected area in the world.

"We will continue to pay attention to the legal actions taken in Galápagos for transport and wildlife traffic. We have a zero tolerance policy," said Ecuadorian environment minister Tarsicio Granizo.

The Galápagos Islands, famous for its giant tortoises, is a chain of 13 main islands with over 1,000 species flora and fauna unique to them.

The Pacific Ocean islands also served as a living laboratory when British naturalist Charles Darwin visited the archipelago in the 1830s and developed his theory of evolution by natural selection.