Nguyen Van Luc, 34, said in a Facebook post that he had told the pair to leave the peninsula on Saturday after refusing to continue showing them around.

He said they had ignored his advice and kept using flashes from a distance of four to five meters from monkeys in the wild.

But they were helped by an Italian woman to continue going around and taking more photos on Saturday evening and Sunday morning, he said.

He called on his colleagues in the Facebook post to stop the duo from using flashes to avoid disturbing the douc langurs.

In an interview with Tuoi Tre newspaper, he said the animals are uncomfortable when flashes go off.

Normally they sit around and eat casually for people to see or take pictures, but immediately move away and seem to panic when a visitor uses a flash from a close distance, he said. Some daring langurs turn their backs to the flashes and continue eating, but move away as soon as they finish, he said.

Luc told his company to terminate the contract with the duo.

Many people, including photographers, voiced strong support for Luc's decision. Some also expressed frustration about the fact the two tourists deliberately used flashes even after being warned.

Son Tra is known for the world’s largest population of the endangered red-shanked douc langur.

Also known as "costumed apes" due to their striking appearance, the monkeys were first detected on Son Tra in 1969. They mostly live in troops of five to 10 at altitudes of 100-600 meters, but some live right by the sea.

Vietnam is home to around 1,000 red-shanked doucs, including less than 300 in Son Tra. The monkeys are threatened by poaching, expansion of agriculture land, and construction to serve tourism. In Son Tra, monkeys would have to cross roads and face the risk of car crashes just to find food.