TOKYO -- Trading volume on the Tokyo Stock Exchange has slumped to the lowest level in 14 years, while Shanghai shares have fallen six weeks in a row, underscoring investor concern over U.S.-China tariff tensions.

Daily trading on the Tokyo bourse's first section averaged 1.5 billion shares in the January-June period, down 20% on the year and the lowest first-half figure since 2004.

The benchmark Nikkei Stock Average closed at 22,304.51 on Friday, up 0.2% from the previous day but down 2% year-to-date.

Fears of an all-out trade war are the main factor behind the lackluster performance, said Hirokazu Kabeya, a stock market analyst at Daiwa Securities. He pointed to signs that the trade tit-for-tat is intensifying, with China and the European Union moving to counter unilateral U.S. tariffs.

"The escalating trade tensions have yet to impact the real economy," Kabeya said. "But they are raising concern about the economic outlook and making investors reluctant to take risks."  

Also hurting market sentiment is the buildup of inflationary pressure in the U.S. This has investors expecting further interest rate increases by the Federal Reserve and an end to the "Goldilocks" global economy of relatively strong growth with low inflation.

Japanese investors are not alone in fretting over the global outlook.

The Shanghai composite index rebounded 2.2% on Friday, to 2,847.41, but it was down 1.5% for the week. The index had entered bear market territory earlier in the week -- a decline of 20% off its recent peak.

Hong Kong's Hang Seng index rose 1.6% on Friday to 28,955.11, but it was down 1.3% for the week, marking the third straight weekly fall. 

The Chinese yuan, meanwhile, briefly touched a seven-month low of 6.6441 against the dollar on the Shanghai foreign exchange market. China is bearing the brunt of tough U.S. trade measures while the American economy continues to perform well, putting pressure on the Chinese currency.