Japan's Nikkei ends at 2-week low as automakers slump on US tariff worries

(Updates with closing prices)

March 28 (Reuters) - Japan's Nikkei average ended at a two-week low on Friday in a broad selloff, with automakers leading the losses, as concerns over the potential impact of U.S. President Donald Trump's trade tariffs weighed.

The Nikkei lost 680 points, or 1.8%, to close at 37,120.33, its lowest close since March 14.

A majority of stocks going ex-dividend resulted in a loss of around 300 points, strategists said.

The broader Topix slipped 2.07% to 2,757.25.

"Uncertainties about the impact of the U.S. tariff plans weighed on sentiment," said Naoki Fujiwara, senior fund manager at Shinkin Asset Management.

Automakers Toyota Motor ( TM ) slumped 4.53%, while Honda Motor ( HMC ) dropped 4.88%. Almost three trillion yen ($20 billion) has been wiped from the market value of Japan's top three carmakers - Toyota ( TM ), Honda ( HMC ) and Nissan ( NSANF ) - in three trading sessions through Friday.

Earlier this week, Trump declared his plan to implement a 25% tariff on imported cars and light trucks, effective from April 3, while the duty on auto parts begins on May 3.

Investors also braced for a wave of reciprocal tariffs that Trump plans to unveil on Wednesday, although he has hinted there may be room for flexibility.

All of the Tokyo Stock Exchange's 33 industry sub-indexes fell, with the brokerage sector falling 4.52% to be the worst performer. The transport index lost 4%.

"Even value shares, which had been supporting local equities, fell today because investors had secured dividend payouts by Thursday," said Fujiwara.

Thursday was the last day for investors to secure rights to dividend payouts for companies with a fiscal year ending in March. Investors scooped up value shares, which pay higher dividends than growth stocks.

Banking shares declined, with Mitsubishi UFJ Financial Group ( MUFG ) and Mizuho Financial Group ( MFG ) and Sumitomo Mitsui Financial Group ( SMFG ) slipping 3.21%, 3.96% and 3.24%, respectively. (Reporting by Junko Fujita, additional reporting by Tom Westbrook; Editing by Sherry Jacob-Phillips and Janane Venkatraman)