The Solomon Islands’ government has voted to sever its longstanding ties with Taiwan and take up diplomatic relations with Beijing.

The move is a huge blow to self-ruled Taiwan, which has lost six allies since 2016, and to Taiwan’s president, Tsai Ing-wen, who is seeking re-election in January amid rising tension with China. It has sparked protests in the Solomon Islands, according to local media.

The Solomon Islands, a country of about 600,000 people in the south Pacific, is the latest country to switch allegiance to China since Tsai came to office in 2016, following Burkina Faso, the Dominican Republic, São Tomé and Príncipe, Panama and El Salvador.

Taiwan announced it was severing ties with the Solomon Islands immediately after learning the Pacific nation had decided to switch diplomatic recognition to China, which it said was “extremely regrettable”.

“We sincerely regret and strongly condemn their government’s decision to establish diplomatic relations with China,” said President Tsai Ing-wen on Monday.

Tsai said Taiwan would close its embassy on Tuesday, lowering its flag at 11:30am local time and recall all technical and medical personnel stationed there.

“It is indeed regrettable that their unfinished cooperative projects must come to an end, and it is a loss for Solomon Islands people. However, this is the choice that Solomon Islands’ government has made, leaving us with no other option but to respond in this way,” she said.

Tsai accused China of engaging in “dollar diplomacy” in the region in order to undermine Taiwan.

“Over the past few years, China has continually used financial and political pressure to suppress Taiwan’s international space,” she said.

China’s foreign ministry spokesman welcomed the decision, saying: “The Chinese side highly appreciates the Solomon Islands government’s decision to ... sever the so-called ‘diplomatic relations’ with Taiwan authorities.”

Taiwan has been a de facto sovereign nation since the end of a civil war in 1949, but China still views the island as its territory and has vowed to bring it under central control.

Over the decades, dozens of countries, including the US and most western nations, have switched recognition to Beijing, leaving just a handful of countries loyal to Taiwan, largely in Latin America and the Pacific.

The decision of the Solomon Islands to switch allegiance followed the recommendation of a taskforce commissioned by the Solomon Islands’ government to investigate the benefits to the country of switching ties. The report, released on Friday, advised that the government switch ties to China and invite it to establish a diplomatic mission in the capital, Honiara, on the island of Guadalcanal.

“The findings reveal that Solomon Islands stands to benefit a lot if it switches and normalises diplomatic relations with PRC [People’s Republic of China],” the taskforce said.

The diplomatic switch reduces the number of countries that recognise Taiwan to 16.

The south Pacific has been a diplomatic stronghold for Taiwan, where formal ties with six island nations made up more than a third of its total alliances, though China has in recent years been expanding its influence in the region.

The Solomon Islands was by far the largest remaining Pacific ally for Taiwan. Its population of 600,000 is larger than all of Taiwan’s remaining allies in the region – Palau, Tuvalu, Nauru, Kiribati and Marshall Islands – combined. The nation has had diplomatic relations with Taiwan for 36 years, during which time it has received considerable financial support from Taiwan.

“This is a hugely significant win for China,” said Anna Powles, a senior lecturer in security studies from Massey University in New Zealand. “The Pacific has increasingly been a bastion of Taiwanese diplomatic support as its allies elsewhere have switched recognition. The Solomon Islands was the largest of these allies and the question is: who will be the next cab off the rank? Taiwan is obviously concerned that this will lead to a domino effect across its remaining Pacific allies.”

Powles said the immediate termination of relations would also have serious implications for existing development programmes in the Solomon Islands, as well as “very human” impacts.

“Development programmes which have been terminated and jobs which will be lost, students who will have to leave Taiwan immediately, relationships which have been formed and have now been severed,” she said.