TAIPEI (Reuters) - Ties between Japan and Taiwan are at their best, Japan’s representative on the island said on Tuesday, at the unveiling of a new name for Japan’s representative office that has riled China.

Japanese Representative to Taiwan Mikio Numata attends a name-changing ceremony of the Japan's de facto embassy from "The Interchange Association, Japan" to "Japan-Taiwan Exchange Association", in Taipei , Taiwan January 3, 2017. REUTERS/Tyrone Siu

Japan and Taiwan have extensive business ties and also share concern about an increasingly assertive mainland China.

But Japan, like most of the world’s countries, maintains only informal relations with Taiwan, which Beijing regards as a renegade province.

Japan has diplomatic ties with Beijing - recognizing China’s position that there is only “one China” and Taiwan is part of it.

“Currently Japan-Taiwan relations are at their best, but we should take further steps to develop a good relationship,” Mikio Numata, Japan’s chief representative, said at a ceremony with Taiwan’s vice foreign minister, Leo Lee.

The ceremony was to officially change the name of Japan’s office on the island - its de facto embassy - to the Japan-Taiwan Exchange Association.

It had been called the “Interchange Association, Japan” since it was set up in the 1970s. Since then, Japan has grown to become Taiwan’s third largest trading partner and second largest source of foreign tourists.

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China has criticized the name change because it includes the word “Taiwan”. Its foreign ministry spokesman Geng Shuang repeated opposition on Tuesday, saying China had lodged representations with Japan about it.

Japan should “not send any wrong messages to the Taiwan authorities or the international community and not cause new interference in Sino-Japan ties”, Geng told reporters in Beijing.

Numata said the name change was to make it clear who the parties were.

“The goal was to put ‘Japan’ and ‘Taiwan’ in the name to clearly point out the counterparts of the exchange,” he said.

Many major countries, including the United States and Britain, operate representative offices in Taiwan under various names. The U.S. mission is the American Institute in Taiwan.

Business relations between the mainland and Taiwan have grown significantly over the past decade but tension has increased since the island elected a president from an independence-leaning party last year.

China distrusts President Tsai Ing-wen and has stepped up pressure on her following a protocol-breaking phone call between her and U.S. President-elect Donald Trump.

Trump later cast doubt on the U.S. commitment to the “one China” policy and on the weekend, he did not rule out meeting Tsai in future.

Geng said there should be no official contacts between the United States and Taiwan.

“The Taiwan issue has always been the most important and sensitive one in relations between China and the United States. We urge the U.S. to fully recognize the sensitivity of the Taiwan issue,” Geng said

“I think that on the relevant issue Trump’s team is very clear.”