Japan's national broadcaster said one of the Chinese maritime surveillance ships had been within a kilometre (1,000 yards) of the fishing boats, in an incident that could inflame a debilitating international row.
There was no attempt by anyone on board to land on any of the islands, which Japan controls as the Senkakus, but which China claims as the Diaoyus.
"The purpose of dispatching the fishing boats is to fish in the waters," an official from the nationalist Channel Sakura satellite broadcaster told AFP, adding the company's president was aboard one of the boats.
The Japanese boats had left the area by the afternoon, he said.
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The incident passed off without confrontation but marked a change from recent months, which have seen regular forays by official Chinese ships into the 12-nautical-mile zone regarded as territorial waters.
It has become customary for Japan's coastguard and the Chinese ships to exchange demands that the other side leave the waters, as part of a tussle between Tokyo and Beijing over ownership of the resource-rich islands.
The four ships made a circuit of the largest island in the chain before heading away, Japan's coastguard said.
A territorial row that dates back four decades reignited last September when Tokyo nationalised three islands in the chain, in what it said was a mere administrative change of ownership.
But the incident provoked fury in Beijing, which maintains the Senkakus were illegally snatched by Japan as it built an empire in the half-century before World War II.
Commentators say the islands are a potential flashpoint for a military confrontation between Asia's two largest powers.
They say the occasional presence of nationalists from both sides introduces a wild card that increases the risk of a misstep by one of the armed official vessels, which could quickly escalate.