Australia is sending police, diplomats and defence personnel to the Solomon Islands to provide stability and security after rioting in the capital Honiara.
Prime Minister Scott Morrison said protests in the capital had become disorderly and a high school, police station and leaf hut adjacent to the parliament had been torched.
"The situation remains volatile with reasonably large crowds on the move," Mr Morrison said.
The deployment, which is expected to last a few weeks, includes a detachment of 23 Australian Federal Police and up to 50 further AFP officers to provide security at critical infrastructure.
In addition, there will be 43 armed defence force personnel, a patrol boat and at least five Department of Foreign Affairs personnel.
An RAAF aircraft left Canberra on Thursday night to carry federal police and DFAT officials in support of Australia's response, the federal government said in a statement.
About 40 defence force personnel will leave Townsville for Honiara on Friday, along with another ADF flight carrying more federal police and DFAT officials which is scheduled to depart Canberra.
A Navy vessel will also be sent to the Solomon Islands, and Australia's response will be scaled up as needed.
All Australian high commission staff and locally engaged staff have been accounted for but the exact number of citizens is not yet known.
"Our purpose here is to provide stability and security," Mr Morrison said.
"We have always been there to help our Pacific neighbours when they need us."
Local police have been "stretched" as anti-government protesters set fire to buildings in the centre of Honiara.
Mr Morrison was adamant the deployment of Australian troops should in no way be seen as the country taking a side in the internal conflict between the Solomon Islands' government and opposition.
"We believe in their sovereignty and we believe in them being able to resolve these issues (democratically)," he said.
Australian police will help local authorities with riot control and defence force personnel will secure critical infrastructure like the airport.
Mr Morrison said the national security committee of cabinet had met just after he received a formal request for support from Solomons Prime Minister Manasseh Sogavare.
Reports and images shared on social media show crowds of protesters and burning buildings in the Chinatown district of Honiara as protesters defied a lockdown in a second day of unrest.
Media reports said people had travelled from the most populous province of Malaita to the capital because of concern about being overlooked by the national government.
The province opposed a 2019 decision to end diplomatic ties with Taiwan and establish formal links with China, resulting in an independence referendum last year which the national government has dismissed as illegitimate.
Mr Sogavare on Wednesday declared a 36-hour lockdown in Honiara after the latest unrest, calling it "another sad and unfortunate event aimed at bringing a democratically elected government down".
The lockdown, which will run until 7am on Friday, would "allow our law enforcement agencies to fully investigate the perpetrators of today's events and to prevent further lawless destruction", Mr Sogavare said.
It is unclear whether China will seek to evacuate its people in Honiara.
In 2006 after Honiara Chinatown was burned down, the Chinese government sent an Air China plane.
© AAP 2021