Japan's trade deficit swelled to a record 1.63 trillion yen (HK$135 billion) on energy imports and a weaker yen, highlighting one cost of Prime Minister Shinzo Abe's policies that are driving down the currency.
Exports climbed 6.4 per cent last month from a year earlier, the first rise in eight months, exceeding a 5.6 per cent estimate.
Imports increased 7.3 per cent, the Finance Ministry said yesterday.
Weakness in the yen, which aids exporters such as Sharp and Sony, also means the country pays more to import fossil fuels needed, as nuclear reactors stand idle after the Fukushima crisis in 2011.
That burden may encourage the government to limit the currency's slide, with Deputy Economy Minister Yasutoshi Nishimura saying last month that a yen at more than 110 per US dollar would raise import costs.
"The trade deficit means the yen can't just keep weakening," said Takeshi Minami, the chief economist at Norinchukin Research Institute.
"Abe will probably restart some nuclear plants after the upper house elections in July as, without them, the costs to the economy are too great."
The yen extended its slide after the data were released, falling 0.2 per cent to 93.73 per dollar in early trading yesterday.
Nearly 80 per cent of Japan's imports were denominated in foreign currencies in the second half of last year, compared with about 60 per cent for exports, according to the Finance Ministry.
Exports to China rose 3 per cent from January last year, the first increase since May, while those to the US gained 10.9 per cent. Shipments to the European Union fell 4.5 per cent.
"A rebound in global demand, especially the US, is helping Japanese exports," Azusa Kato, an economist at BNP Paribas, said before the data.
The Finance Ministry said trade balance tended be weaker in January as the New Year holiday slowed production and crimped exports.
Japan's government predicts that trade with China, the nation's biggest export destination, will recover this year after falling last year for the first time in three years because of a territorial dispute and a slowdown in the Chinese economy.