Trump leaves for G20 with attacks on China, allies

President Donald Trump waves before walking up the steps of Air Force One at Andrews Air Force Base in Maryland. Trump is heading to the G-20 in Japan. (AP Photo/Susan Walsh)

Air Force One took off on a fiercely hot day from Washington and Trump seemed to promise heat of his own when he meets leaders of the G20 countries in Osaka, Japan, before stopping over in South Korea.

Declaring that he enjoys a strong hand in the trade war with China, he made clear he'll be in no mood to give much ground when he holds closely watched talks with President Xi Jinping on Saturday.

"China's economy is going down the tubes - they want to make a deal," Trump said in an interview with Fox Business Network.

Trump has already hit US$200 billion of Chinese imports with levies in an effort to force Beijing into intellectual property protection and other reforms of a trading system that Washington says gives China huge unfair advantages.

The president indicated he was also ready to slap tariffs on all remaining Chinese imports - more than US$300 billion worth.

"You have another US$325 billion that I haven't taxed yet - it's ripe for taxing, for putting tariffs on," he told Fox.

According to Trump, it's China that's feeling all the pain, while the US side is benefiting from the situation.

"What is happening is people are moving out of China. Companies are moving out of China, by the way, some are coming back to the United States because they don't want to pay the tariff," he told Fox Business Network.

Trump did say that a previous threat to tax this remaining segment at 25 per cent could be changed to a less harsh 10 per cent.

The two sides said they were close to a deal before talks broke down in May.

"We were about 90 per cent of the way there," Treasury Secretary Steven Mnuchin told CNBC television, saying he was looking forward to the Trump-Xi talks but stressing there would be no deal for "the sake of a deal."

"I hope the message that we want to hear is that they want to come back to the table," Mnuchin said.

TRUMP ON DIPLOMATIC WARPATH

Trump's aggressive attempt to rewrite the rules with China are part of a wider policy of fixing what he says is a system rigged against the United States.

"Almost all countries in this world take tremendous advantage of the United States. It's unbelievable," he said in the lengthy Fox interview.

Casting his eye over the wider landscape, Trump also lashed out at close partners Vietnam, Germany and Japan.

Vietnam is "even worse than China" when it comes to unfair trading practices, he said. Vietnam is the "single worst abuser."

He described Germany - part of the bedrock of the US alliance with western Europe - as "delinquent" for not paying enough to NATO's budget.

"So Germany is paying Russia billions and billions of dollars for energy, okay," he said. "So they are giving Russia billions of dollars yet we are supposed to protect Germany and Germany is delinquent! Okay?"

Trump aired a similar complaint about Japan, Washington's closest ally in Asia, which has been under the protection of a US military umbrella since its defeat in World War II.

"If Japan is attacked, we will fight World War III. We will go in and protect them with our lives and with our treasure," he said. "But if we're attacked, Japan doesn't have to help us. They can watch it on a Sony television."

Speaking to reporters at the White House, Trump remained coy on expectations for his meeting at the G20 with Russia's President Vladimir Putin.

Trump has been criticised for what opponents see as an oddly opaque relationship between the two leaders and he did little to dispel the controversy.

"I'll have a very good conversation with him," Trump told reporters. "What I say to him is none of your business."

On another intrigue-filled front, Trump said he would not be meeting with North Korea's strongman leader Kim Jong Un, but said "I may be speaking to him in a different form."

Trump has held two summits with Kim in a bid to persuade him to let go of his nuclear arsenal and end his country's isolation. So far, the policy has had little success.