President Donald Trump is reportedly set to involve Japan in his trade war, saying he will make the world's third-largest economy "pay."

According to a report from the Wall Street Journal late on Thursday, Trump indicated to reporter James Freeman that he is ready and willing to hit Japan with tariffs.

Japan imported over $40 billion of cars into the US last year.

The report comes as the US prepares to impose fresh tariffs on up to $200 billion of Chinese goods.

US President Donald Trump may not be entirely done with his trade war against China, but it looks as though he already has another target in his sights: Japan.

According to a report from the Wall Street Journal late on Thursday, Trump indicated to reporter James Freeman that he is ready and willing to make Japan "pay" going forward, suggesting that tariffs on Japanese goods may be on their way.

Writing in an opinion piece, Freeman says he received a phone call from the president following an appearance on Fox News, during which Trump "described his good relations with the Japanese leadership but then added: 'Of course that will end as soon as I tell them how much they have to pay.'"

During his trade salvos, Trump has imposed tariffs on China, the EU, Canada and Mexico. But so far he has only threatened to involve Japan, without actually engaging it.

That now looks set to change, if Freeman's conversation with the president holds true.

Japan, the world's third-largest economy after the US and China, is a major trading partner for the US, with automobile imports particularly important.

Major Japanese brands like Toyota and Honda send more than 8 million cars to the US each year, and manufacture close to 4 million within the US. Last year, more than $40 billion of Japanese autos entered the country.

Trump has previously lamented that imported vehicles are a threat to national security, with Japanese Prime Minister Shinzo Abe one of the strongest dissenting voices against such claims.

"Imports of our nation’s automobiles and auto parts have never damaged U.S. national security and will not do so in the future," Abe said at a news conference in July.

"Trade restrictions will not benefit anyone, and we will keep explaining that to the U.S. and work closely with them to ensure those tariffs are not imposed," he added.

Reports of Trump's willingness to engage Japan in his trade war come just hours before the US is expected to make public its decision on whether to levy fresh tariffs on a cumulative $200 billion worth of Chinese goods imported to the USA.

A consultation period on introducing the new tariffs ended overnight, and it is widely expected that they will be imposed. The tariffs could be set at a level of 10% or 25% depending on the recommendation of the United States trade representative.

The new tariffs, affecting roughly 40% of all Chinese exports to the US, would mark the biggest escalation of the trade conflict so far and would be almost guaranteed to lead to retaliatory tariffs from the Chinese government.