By Nick Bryant BBC News, Sydney

Mr Howard urged activists not to engage in violent protests

Australian Prime Minister John Howard has posted a video on YouTube appealing to people not to join violent protests during the Apec summit in Sydney.

The city is hosting the gathering of 21 world leaders amid massive security.

Some are calling it Fortress Sydney, such is the scale of the operation to protect Australia's biggest ever gathering of world leaders.

Protest-proof fences have been erected close to the Opera House and other sites where meetings are taking place.

Patrol boats have also been zipping across the harbour.

New frontier

Demonstrators have vowed to disrupt the summit, with large street protests planned throughout the week.

If they really are worried about issues such as poverty, security and climate change, then they should support Apec, not attack it John Howard Watch the YouTube video Send us your comments

But John Howard has sought to pre-empt them by appearing on the popular internet site YouTube and appealing for their co-operation.

Mr Howard is often described by opponents as a politician from the black-and-white television age, so his online statement is something of a departure.

Effectively, he is confronting the protestors on their own turf - the internet.

"There will be some individuals who want to protest against Apec," he says in the video.

"I simply ask them to stop for a moment and consider that if they really are worried about issues such as poverty, security and climate change, then they should support Apec, not attack it."

With the summit bringing together the world's three most voracious energy consumers - America, China and Russia - Mr Howard has placed climate change at the top of the agenda.