The BBC has the details:
“On 30 January, something like fire-control radar was directed at a Japan Self-Defence Maritime escort ship in the East China Sea,” Mr Onodera told reporters on Tuesday.
The minister said Japan’s Yuudachi vessel and the Chinese frigate were about 3km (one mile) [ed: conversion error here, 3km is about 2 miles] apart at the time, Japan’s Kyodo News reports.
Asked about the delay in filing the protest, Mr Onodera said it took the ministry until Tuesday to determine that a fire-control radar had indeed locked on the Japanese ship.
He added that a Japanese military helicopter was also targeted with a similar type of radar by another Chinese frigate on 19 January.
“Directing such radar is very abnormal. We recognise it would create a very dangerous situation if a single misstep occurred,” he said.