TOKYO, May 24 (Reuters) - Japan's Nikkei share average fell to more than two-week lows on Thursday as automakers slumped after the Trump administration launched a national security investigation into car and truck imports that could lead to new U.S. tariffs.
The Nikkei ended 1.1 percent lower at 22,437.01, the lowest closing since May 9.
The Nikkei volatility index soared to 18.29, the highest level since mid-April.
The transport equipment sector tumbled 3.0 percent and was the board's worst performer after news of the U.S. probe.
Toyota Motor Corp fell 3.1 percent, Subaru Corp dropped 2.5 percent and Mazda Motor Corp plunged 5.2 percent.
Nissan Motor Co and Honda Motor Co shed 1.8 percent and 3.4 percent, respectively.
"Sentiment in the auto sector is bad with the tariff concerns, and a strong yen is pouring salt on the wound," said Takashi Ito, equity market strategist at Nomura Securities.
The dollar weakened 0.5 percent to 109.54 yen in Asian trade, a day after the greenback lost 0.73 percent, its biggest fall in nearly three months.
GS Yuasa, which makes automotive lithium-ion batteries with Honda, stumbled 4.5 percent after the Nikkei business daily reported that the automaker will team up with Contemporary Amperex Technology, the world's largest battery maker, to develop electric vehicle batteries that it seeks as key to its global strategy.
Discount clothing chain Shimamura dived 5.8 percent after its May same-store sales dropped 7.7 percent on the year due to cold weather.
The broader Topix dropped 1.2 percent to 1,775.65. (Editing by Richard Borsuk)