* Nikkei posts longest spell of losses since late January
* Topix down for seventh straight day
* Advantest, Tokyo Electron tumble
By Ayai Tomisawa
TOKYO, Sept 7 (Reuters) - The Nikkei extended its decline to a sixth straight session on Friday, dropping to a 2-1/2-week low as investors sold chip equipment makers and fretted over reports that U.S. President Donald Trump could be contemplating taking on Japan over trade.
Global markets were already on edge amid fears that the United States and China could launch another round of tit-for-tat tariffs anytime as a public comment period on U.S. measures ends.
The benchmark share average dropped 0.8 percent to 22,307.06, its lowest closing level sine Aug. 21. The index was down for the sixth day running, its longest losing streak since late January.
For the week, the Nikkei tumbled 2.4 percent, its biggest weekly fall since mid-March.
The broader Topix declined 0.5 percent to a more than three-week low of 1,684.31 to post a seventh consecutive day of declines.
The market was spooked after CNBC reported that Trump had told a Wall Street columnist that he will take his global trade fight to Japan.
"Investors were worried that sooner or later, Japan's auto industry would be Trump's target and now they are bracing for more details," said Takuya Takahashi, a strategist at Daiwa Securities.
"The mood has deteriorated as the market was already nervous with U.S.-China tariff issues."
Exporters' shares were under pressure, with Subaru Corp declining 2.4 percent, Kyocera Corp tanking 3.8 percent and Panasonic Corp falling 1.6 percent.
Chip equipment makers weighed on the benchmark index, after KLA Tencor tumbled 9 percent after Chief Financial Officer Bren Higgins said September was still "a drought for DRAM" and that a pick-up in business later this year would be less than expected.
Advantest Corp dived 7.2 percent and Tokyo Electron tumbled 6.0 percent. High-purity silicon maker Sumco Corp declined 5.2 percent and Shin-Etsu Chemical shed 2.7 percent. (Editing by Kim Coghill and Sunil Nair)