Legislators have appointed political veteran Manasseh Sogavare as the Prime Minister of Solomon Islands — for the fourth time — but his victory has already stoked tensions in the capital Honiara.

Key points: Mr Sogavare won three times before in 2000, 2006 and 2014

Mr Sogavare won three times before in 2000, 2006 and 2014 Australia undertook a 14-year security mission in the Solomon Islands until 2017

Australia undertook a 14-year security mission in the Solomon Islands until 2017 It is rare for a Solomon Islands PM to serve a full term

Several MPs opposed to Mr Sogavare sought an injunction against the ballot and walked out of the vote when they failed to stop it.

Protests have also broken out in parts of Honiara, with police using tear gas to dispel angry crowds near China Town and in a settlement in the city's east.

Police said nine officers were injured in the protests, and more than 30 protesters had been detained so far, with more arrests expected.

Mr Sogavare is a familiar face who is used to the uncertainties of Solomon Island politics. ( Reuters; Eduardo Munoz, file photo )

The election is a crucial test of stability on Solomon Islands, and Australian officials are watching events very closely.

Mr Sogavare's victory this morning was controversial.

His main opponent, Matthew Wale, argued Mr Sogavare may not be eligible to be Prime Minister because he registered his political party late.

The High Court ordered the contest for the position should be postponed, but Governor-General Sir Frank Kabui used constitutional powers to press ahead with the vote.

Mr Wale and about 15 supporters responded by walking out.

In the end only 35 ballots were cast, with all but one of them in favour of Mr Sogavare.

Hundreds of police deployed

A large crowd of protesters moves across the newly opened China Town bridge in Honiara. ( Supplied: Danzo Photography )

Not long after that protests broke out in parts of Honiara, with a small group of young men marching to Parliament House and calling for Mr Sogavare to step down.

Royal Solomon Islands Police Force (RSIPF) Commissioner Matthew Varley said in a video statement posted to Facebook he had ordered "a large number" of roadblocks and checkpoints to be put in place across the city.

Mr Varley said he had directed police, including the riot squad, to "take stern and swift action" against anyone found to be participating in "illegal activities".

Riot police were among the officers deployed across Honiara in response to the post-election unrest. ( Supplied: Danzo Photography )

Commissioner Varley also appealed for people to accept the election outcome, and vowed that police would step up patrols of Honiara overnight to guard against unrest.

"I urge all law-abiding citizens to stay at home tonight and stay off the streets. Please stay home with your families tonight and allow the police to maintain law and order in our capital city," he said.

Videos posted to social media showed large crowds of young men walking through the streets near China Town while yelling slogans and throwing objects.

Photographs show damage to the kitchen and other areas of the Pacific Casino Hotel in Honiara, which was reportedly trashed by rioters. ( Supplied: SIBC )

Large numbers of police turned them back from the area, which was the site of violent riots back in 2006.

Meanwhile, police have reportedly used tear gas to disperse crowds in Kukum, in Honiara's west.

The Solomon Islands Broadcasting Corporation also reported that rioters had trashed the Pacific Casino Hotel, posting pictures which showed smashed windows, as well as computers and other equipment strewn all over the ground.

Police said numerous vehicles were also damaged.

Police said that at least nine officers were injured in the demonstrations. ( Supplied: Danzo Photography )

One Australian Government source told the ABC officials from DFAT were closely monitoring events in Honiara.

Australia played a major supporting role in ensuring the election went smoothly when voters went to the poll earlier this month.

The election was the first since the Australian-led 14-year-long security mission known as Regional Assistance Mission to Solomon Islands (RAMSI) came to an end in 2017.

The operation brought stability to the country after years of ethnic violence, and Australian officials are hoping the current unrest in Honiara subsides quickly.

Windows were smashed at the Pacific Casino Hotel, while computers and other equipment were strewn all over the ground. ( Supplied: SIBC )

PM promises to get back to work

Mr Sogavare is a familiar face who is used to the mercurial uncertainties of Solomon Island politics.

He has already won the top job three times before in 2000, 2006 and 2014, and has been ousted from the position twice.

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In 2017 MPs used a vote of no confidence to remove Mr Sogavare after he tried to push through new rules to fight corruption.

Mr Sogavare's experience is not unusual in the Solomon Islands.

Governing coalitions in the country are notoriously fragile, and it is rare for a PM to ever serve a full term.

Australian National University researcher Terence Wood said Mr Sogavare's victory demonstrated his political resilience and agility.

"Solomon Islands politics is very fluid, and as an experienced power player he's been able to overcome setbacks" Mr Wood said.

Mr Sogavare used his first speech to say God had delivered him victory and promise to get down to work quickly.

"The Government will go straight into allocating our various portfolios and get straight into the business of running the affairs of the state," he said.