The government is planning to lodge a stronger protest with Beijing over the repeated presence of Chinese survey ships in Japan's exclusive economic zone, Chief Cabinet Secretary Hiroyuki Hosoda said Wednesday.

"We have to raise a stronger protest," Hosoda, the government's top spokesman, told a news conference.

A 1,040-ton Chinese Navy survey vessel was spotted Tuesday in the EEZ, some 40 km west of the disputed Senkaku Islands, which are claimed by both countries.

Meanwhile, a 3,536-ton Chinese government marine research ship was found the same day in the EEZ, some 340 km southwest of Okinodaito Island in Okinawa Prefecture.

The ships were apparently conducting oceanographic surveys, according to the Maritime Self-Defense Force, whose P-3C patrol airplanes spotted the Chinese vessels in waters southwest of the Japanese archipelago.

Japan had earlier spotted another Chinese naval ship, as well as the government ship, in its EEZ waters several times this month alone.

When a 3,141-ton Chinese marine research ship was repeatedly spotted in the EEZ without prior notice in mid-May, the Foreign Ministry lodged its third protest in the space of a week with China.

In February 2001, Japan and China agreed to give each other two months' prior notification with regard to maritime scientific research activities in waters around the two countries.