Comment: For those unfamiliar, 'fishers' is the archaic form of fisherman, although it's likely that The Guardian is reviving it for 'gender-neutral' purposes.
The Kinmen islands lie within a few miles of China's Fujian coast and are controlled by Taiwan.
The Chinese speedboat was carrying four people when it capsized on Wednesday, throwing all onboard into the water, Chinese and Taiwanese authorities said.
"The malignant incident severely harmed the feelings of compatriots on both sides of the Taiwan strait," Zhu Fenglian, a spokesperson for China's Taiwan affairs office, said in a statement.
Taiwan's coastguard said the speedboat had "illegally [entered] Taiwanese waters", Taiwan's Central News Agency (CNA) reported.
The coastguard "immediately requested that the boat submit to an inspection, but it resisted and capsized as it sped away", CNA said.
Comment: One suspects it capsized as the coastguard was chasing them.
CNA said all four were rescued from the water and sent to hospital. "Two were pronounced dead after efforts to resuscitate them failed," the coastguard said. "The other two are in stable condition and have been brought to Kinmen for further investigation by prosecutors."
Beijing has urged the Taiwanese authorities to immediately investigate the incident, Zhu added.
In response, Taiwan's mainland affairs council reiterated support for Taiwanese authorities "enforcing the law" and said it "deeply regretted the unfortunate incident that occurred when the mainland crew refused to cooperate".
It said a preliminary investigation found that the coastguard personnel had performed their duties in accordance with the law, and that processes were "not improper".
The statement said that in recent years a small number of people from the mainland had crossed into Taiwanese waters to conduct sand dredging, dumping of refuse or fishing activities that damaged the marine environment. It added that in the past few days many fishing boats registered to China had entered Taiwan's waters to catch high-value fish during the lunar new year.
"Our people have repeatedly lodged reports and the competent authorities are required to carry out expulsions in accordance with the law, and coastguard personnel have an unshirkable duty to strengthen law enforcement in order to safeguard people's rights," it said.
The incident comes against a backdrop of high tensions across the Taiwan strait. China's ruling party claims Taiwan as a province, which it intends to annex. Taiwan's government says Taiwan is an independent nation and a growing majority of its people reject the prospect of Chinese rule.
Taiwan's presidential election, held in January, was won by the ruling Democratic Progressive party's Lai Ching-te, whom Beijing regards as a "separatist".
Xi Jinping, China's leader, has repeatedly called for the "reunification" of Taiwan with China, which split nearly 75 years ago at the end of a civil war in 1949.
The boating incident prompted angry reaction on Chinese social media, where related hashtags drew millions of engagements, with some calls for a stronger reaction by Beijing. Official state media did not prominently display the news online.
Comment: Arnaud Bertrand explains the possible significance of this incident; however, as shown in the response that follows, it's possible that these weren't fishermen: Either way, US provocations in the region make for a very tense situation indeed. However, over many years Russia has repeatedly shown, in the face of brazen attacks by the US, and its proxy Ukraine, that the multipolar world are in it for the long game, and, unlike the desperate West-Israel, they aren't going to throw it all away with rash miscalculations.