As the people of Hong Kong usher in the Year of the Monkey, animal experts are working to quell their exploding numbers in a bid to keep the peace between them and their human neighbours.

Hong Kong's hillside monkey colonies are a popular draw for tourists and locals, but after reports of them stealing children's lunches, running amok in a school yard and shoplifting bread, some are fed up with the pesky primates.

In 2007, the government introduced a programme to control reproduction, via surgery, among the mischievous creatures.

"The overarching goal is to minimise conflict between humans and animals," said government veterinarian and monkey expert Paolo Martelli, who works in the contraception programme.

While numbers are down thanks to the control measures, hikers in Hong Kong's parks are divided over whether the monkey is a bonus or blot on the landscape.

"If we don't feed them, they pester us," said Easter Liu, 56, on the Kam Shan trail in the city's north, known as "monkey mountain".

Primates there roam freely in the trees, unafraid of passing walkers.

"I think the monkeys are multiplying way too fast, faster than the population of Hong Kong, I feel a threat," said Liu, an IT sales worker, still upset that a monkey once stole her ice cream.

Architect Tony Tsang, 44, was also a bit shaken after being attacked by a monkey for the potato crisps and instant noodles he was carrying.

"My first impression was that they were really friendly, but when they heard the sound of the bags they got ferocious and the experience was a bit scary," Tsang told AFP.

- Long history -

Others defend the monkeys as part of Hong Kong's history -- and experts say humans are to blame for their bad behaviour and rising numbers by feeding them.

As a result of human contact, the monkeys have become more aggressive and feeding has improved the survival rate of younger macaques, boosting numbers.

"As a child I came here to see the monkeys... it's quite special," said Patrick Lau, 40, who works as a museum curator and was visiting Kam Shan with his two young children.

"It's not like viewing animals in a zoo -- you can interact with the monkeys quite closely," Lau said.

Hong Kong's indigenous rhesus macaques were last seen in the 1950s -- the island's current colonies are descendents of imported monkeys in 1910 and released near a reservoir to eat plants that were poisonous to humans. The government has no record of where they came from.

The current monkey troops are mostly made of up of rhesus and long-tailed macaques, and their hybrids.

Numbers are now around 2,000 due to the programme, down from en estimated 2,400 in 2009. Population figures were not recorded before then.

- 'Human problem' -

Veterinarians travel twice a month to Hong Kong's country parks to perform painstaking sterilisation surgeries.

They lure the monkeys into "feeding cages" before injecting a sedative, performing the operation, and then releasing the animals unharmed within a few hours.

Animal rights workers concede this procedure is necessary until humans change their habits.

"The reality is this is a human encroachment problem, but if society refuses to fix that problem, sterilising wildlife that has nowhere to go is a sad compromise," PETA vice-president of international operations Jason Baker told AFP.

A ban on the public feeding of the monkeys was introduced in 1999 in another bid to control the growing population.

Authorities also planted 200,000 fruit trees in monkey habitats in the early 2000s to increase their dependency on natural food sources.

However, walkers still take to the trails with peanuts and bananas, despite signs telling them not to feed the animals.

"This problem would not exist if people were not coming to feed the animals," Martelli said.