Australia's military began culling hundreds of kangaroos at a defence base near the nation's capital on Friday, enraging animal rights activists who vowed to stop the killings.

Authorities say the animals threaten other local species through overgrazing.

A handful of protesters were watched by police today.

"We are expecting hundreds of people and if they start killing them we'll be going inside the fence. We will have a 24-hour guard on them," said Wildlife Protection Association spokesman Pat O'Brien, adding the cull could damage tourism.

The eastern grey kangaroos, which feature on Australia's coat of arms, are living on a military communications base on the outskirts of Canberra.

Defence spokesman Brigadier AndrewNikolic said around 400 out of nearly 600 kangaroos at the 200 ha (495 acres) site would be killed after the government ruled out a resettlement programme as too expensive.

After more than a year of indecision amid international protests, including one by a British animal protection group using the face of former Beatle Paul McCartney, military chiefs said they had no option other than to kill the native animals.

"It is humane treatment and in accordance with the contract. It has to comply with the national code of practice for humane destruction of kangaroos," Nikolic said.

McCartney in March appeared on a website set up by the British animal welfare group Viva! to condemn the cull and protect the kangaroos from "shameful massacre".

Viva!, or Vegetarians International Voice for Animals, launched a Europe-wide campaign against the cull, attracting thousands of protest signatures from Spain, Britain, the United States, Switzerland, France, Canada, South Africa and Germany.

In 2004 there was an international outcry over the shooting of 900 kangaroos at a dam supplying water to Canberra. The animals were causing erosion problems through grazing.