The Nikkei stock index ended at a nearly six-month high on Thursday, approaching its pre-pandemic levels amid growing hopes for the development of a vaccine against the novel coronavirus.

The 225-issue Nikkei Stock Average ended up 405.65 points, or 1.78 percent, from Wednesday at 23,249.61, its highest closing level since Feb. 21. The broader Topix index of all First Section issues on the Tokyo Stock Exchange finished 18.62 points, or 1.16 percent, higher at 1,624.15.

Gainers were led by precision instrument, electric appliance and pharmaceutical issues.

The U.S. dollar stayed firm in the upper 106 yen zone as higher U.S. stocks improved risk appetite among investors, dealers said.

At 5 p.m., the dollar fetched 106.63-65 yen compared with 106.86-96 yen in New York and 106.78-80 yen in Tokyo at 5 p.m. Wednesday.

The euro was quoted at $1.1827-1828 and 126.11-15 yen against $1.1779-1789 and 125.93-126.03 yen in New York and $1.1748-1749 and 125.45-49 yen in Tokyo late Wednesday afternoon.

The yield on the benchmark 10-year Japanese government bond fell 0.005 percentage point from Wednesday's close to 0.030 percent as investors bought back the debt. Traders earlier sold the safe-haven asset after brisk U.S. consumer price data for July added to expectations of an economic recovery.

Wall Street lifted overnight after the U.S. government and Moderna Inc. agreed that the biotechnology company would supply 100 million doses of its potential coronavirus vaccine.

The Nikkei briefly rose over 2 percent in the afternoon, topping 23,300, just below levels seen before it plunged in late February amid an escalation in the coronavirus outbreak.

"The market welcomed the higher U.S. shares amid expectations that the Japanese economy will rebound by benefitting from a U.S. recovery," said Masahiro Ichikawa, senior strategist at Sumitomo Mitsui DS Asset Management Co.

A weaker yen was also a positive factor, pushing up exporter issues including precision instrument, electric appliance, and machinery.

But Maki Sawada, vice president of the investment research and investor services department at Nomura Securities Co., said the upward momentum will likely prove short-lived.

"Uncertainty remains over the development of a vaccine, such as possible adverse effects, and it is expected to require more time to become widely available in Japan," Sawada said.

On the First Section, advancing issues outnumbered decliners 1,478 to 615, while 80 ended unchanged.

Among precision instrument makers, Olympus climbed 80.00 yen, or 3.8 percent, to 2,160.00 yen, Nikon advanced 19 yen, or 2.3 percent, to 838 yen, while Terumo jumped 182 yen, or 4.5 percent, to 4,271 yen.

Chip-related issues rose, tracking gains among U.S. counterparts on Wednesday.

Advantest gained 230 yen, or 4.3 percent, to 5,580 yen, Tokyo Electron climbed 865 yen, or 3.1 percent, to 28,705 yen and Lasertec soared 570 yen, or 6.7 percent, to 9,040.

Trading volume on the main section fell to 1,411.49 million shares from Wednesday's 1,491.13 million shares.

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