* Toyota falls after Trump threatens on Mexico manufacturing plans
* Fast Retailing contributes hefty negative 91 points to Nikkei
* Nikkei up 1.8 percent so far for week
By Ayai Tomisawa
TOKYO, Jan 6 (Reuters) - Japan's Nikkei share average dropped on Friday morning as automakers dragged after incoming U.S President Donald Trump threatened to slap punitive taxes on Toyota cars imported into the United States from Mexico.
Index heavyweight Fast Retailing also dragged on the market after reporting weak monthly sales.
The Nikkei fell 0.4 percent to 19,439.24 in midmorning trade, after hitting as low as 19,354.44 earlier, although the benchmark index is up 1.8 percent for the week so far.
Fast Retailing Co dived 5.6 percent and contributed a hefty negative 91 points to the benchmark index after saying that same-store sales at its Uniqlo clothing outlets in Japan fell 5 percent in December from a year earlier.
Toyota Motor Corp fell more than 3 percent at one point after Trump threatened to impose heavy taxes on the automaker if it builds its Corolla cars in Mexico for the U.S. market.
Other Japanese carmakers also fell, with both Honda Motor Co and Nissan Motor Co falling more than 2 percent.
Analysts said that investors are focused on U.S. jobs data due out later in the day, and overall trading will likely be subdued before a long weekend in Japan.
Markets in Japan will be closed on Monday for a national holiday.
"In the near-term, investors are looking at the volatile dollar-yen moves," said Nobuhiko Kuramochi, a strategist at Mizuho Securities.
That said, the current dollar-yen levels are still favourable for Jan-March earnings for Japanese exporters, which had expected a much stronger yen, Kuramochi added.
"The Nikkei is likely to gain further in the next few weeks on hopes that companies' earnings will be stronger than expected," he said.
At 0147 GMT, the dollar rose 0.6 percent at 116.02 yen after falling 1.6 percent overnight.
The broader Topix dropped 0.4 percent to 1,549.92 and the JPX-Nikkei Index 400 fell 0.4 percent to 13,899.25.
Reporting by Ayai Tomisawa; Editing by Eric Meijer