John Howard, the Australian prime minister, said at a joint news conference the day before with Helen Clark, his New Zealand counterpart, that Australia was committed to maintaining stability in the region.
"Being the largest and wealthiest countries in the region, part of our responsibility is to help," Howard said from Hanoi, where he is attending the Asia-Pacific summit.
Clark said the New Zealand troops would focus on providing security at Tonga's Fau'amotu International Airport. Air New Zealand has cancelled its flights to Tonga until Sunday.
Police said the capital, Nuku'alofa, was fairly calm on Saturday although two more shops on the outskirts of the city had been set alight overnight.
Sinilau Kolokihakaufisi, a police commander, told Reuters: "The situation is relatively calm and law and order seem to be restored."
The rioting began after parliament went into recess for the year without voting on proposals for sweeping democratic reforms to Tonga's semi-feudal system.
Late on Thursday, the government bowed to the protesters and agreed to new elections in 2008 in which a majority of the parliament would be directly elected by popular vote.
At present, nobles and appointed MPs outnumber elected representatives.