Two American nationals were arrested in Japan after a stunt in which one entered the monkey enclosure at a zoo where a baby macaque named Punch became a global internet sensation this year, police said Monday.

One of the men, who identified himself as a 24-year-old college student, was arrested Sunday after climbing over a fence and dropping into a dry moat surrounding the monkey exhibit at Ichikawa City Zoo outside Tokyo.

The other man, who was filming the act, identified himself as a 27-year-old singer.

Images on social media showed a person scaling the fence in a costume that included a smiley face head with sunglasses, prompting the monkeys to scatter. 

The men did not come close to the animals, and were quickly apprehended by zoo officials, said an official at Ichikawa Police who spoke with AFP on a traditional condition of anonymity.

The two men face charges of forcible obstruction of business, which they refute, the police official said.

The duo did not have formal identifications with them and initially tried to lie to police about their names, he added. 

The arrests follow a massive surge in domestic and international visitors to the zoo, driven by Punch's viral fame.

The baby monkey became an internet star this year after the zoo posted photos of Punch clutching an IKEA plush orangutan for comfort after being rejected by his mother.

Punch was raised in an artificial environment after being born in July, and began training to rejoin his troop earlier this year.

Punch's predicament sparked huge interest online, spawning a devoted fanbase under the hashtag #HangInTherePunch.

An unprecedented number of tourists are flocking to Japan, but some residents have become fed up with unruly behaviour.

Last year, a Ukrainian YouTuber with more than 6.5 million subscribers was arrested after livestreaming himself trespassing in a house in the Fukushima nuclear exclusion zone.

And a US livestreamer known as Johnny Somali was arrested in 2023 for allegedly trespassing onto a construction site.