Key Points:

A joint New Zealand-Australian task force will arrive in riot-torn Tonga this afternoon

An air force Boeing is due to arrive in Tonga at 3pm.

Commander Joint Forces New Zealand, Rear Admiral Jack Steer said the New Zealand contingent included a 62-strong New Zealand Defence Force (NZDF), a small contingent of New Zealand Police and other Government personnel.

Two C130 Hercules would transport additional cargo and up to four light operational vehicles, he said.

A further 80 Australian Defence and Federal Police personnel would join the NZDF contingent in assisting the Tongan government as part of a New Zealand led Combined Joint Task Force.

The contingent would provide security to the Fau'amotu international airport to enable the resumption of civilian air travel, he said.

New Zealand had taken the lead role in a combined operation with Australia but both countries had deployed jointly to a number of regions within the pacific and had worked very well together, Admiral Steer said.

"This is an opportunity for NZDF to take a leadership role in this type of operation and I have complete faith that they will carry out their role professionally."

Helen Clark and John Howard earlier this morning expressed hope that the joint deployment of troops and police to riot-torn Tonga by New Zealand and Australia would be a short-term pre-cautionary measure.

"We hope that we can see just a short presence by both Australia and New Zealand," Howard said.

"The reason why I'm reasonably hopeful they won't be there for very long is that it has not been the habit or the custom of the people of this country to resort to violence.

"They are not by nature a violent people - quite the reverse."

A pro-democracy march on Thursday ended in a riot that left up to 80 per cent of central business district of the capital, Nuku'alofa, burned and at least eight people dead.

The announcement of the deployment, which will be New Zealand-led, was made at 1.15am NZT by both Prime Ministers in a joint press conference in Hanoi where other leaders are attending the Apec summit.

It is understood that Tongan Prime Minister Feleti Sevele decided at an early stage to request assistance from the two Pacific powers.

But the new monarch, King George Tupou V, was initially resistant.

The priority for the New Zealand's Defence Force will be to secure the airport. Air New Zealand and Polynesian Airlines suspended refused to land at Fua'amotu International Airport because of the uncertain security situation.

Helen Clark said the New Zealand Police would focus on security at the High Commission but among them would be a small number who could make an assessment of what further policing needs Tonga might have.

Tonga had found that its own forces had been stretched to the limit of its capacity and that it was too stretched on law and order elsewhere to maintain the security of the airport.

"It is absolutely critical for any return of normality that people can come and go from Tonga," said Helen Clark.

She said Tonga had been pretty quiet yesterday so hoped the deployment would not be for long.

It was "a preventive measure now" to give some assurance that things wouldn't get out of control again.

Howard described Australia and New Zealand's response as "our responsiblity."

"Being the largest and wealthiest countries in the region, part of our responsibility is to help.

"These are our friends, our neighbours, our Pacific partners, and of course we want to and need to and should help them. It is an act of, probably generosity. The rest of the world would expect it," he said.

In return he expected a higher level of governance.

But he said Tonga was different to the Solomon Islands - where Australia leads another joint deployment.

Helen Clark said there were two futures on offer for the Pacific.

"One is poverty and conflict; the other is peace and development."