President Donald Trump will depart on his longest overseas trip yet on Friday, embarking on a 12-day visit to Japan, South Korea, China, Vietnam and the Philippines following a brief stop in Hawaii. Instead of appeasing the Asian allies he was slated to visit, or previewing the discussions he planned to have, he shot Japan a warning about the North Korean nuclear threat.

“Of course they’re worried,” he told Fox News’ Laura Ingraham on Thursday when she prodded him about Japan, which is located only about 650 miles from the rogue regime. “They should be worried. You know, they’re very close to North Korea.”

Japan is a U.S. ally and Prime Minister Shinzo Abe is “a very good friend” of his, Trump continued. It’s a “warrior nation,” he warned, “and I tell everyone else that, listen, you’re going to have yourself a big problem with Japan pretty soon if you allow this to continue with North Korea.”

Brendan Smialowski/AFP/Getty Images Shinzo Abe, Japan's prime minister, and U.S. President Donald Trump talked during the United Nations General Assembly in New York City in September. They will see each other again during Trump's trip to Asia.

He then struck a more positive tone, praising the close relationship he’s developed with Chinese leader Xi Jinping, who has been, per Trump, “pretty terrific.”

The Trump administration has taken an unprecedented tack on dealing with the North Korean nuclear threat, demanding that China share the burden and leverage its influence over the rogue nation. Trump’s hopeful, he said, that the issue can be solved.

“I think a lot of good things are going to happen. I think it’s a very important trip. I think this is one of the more important trips that a president has made.”

Carlos Barria/Reuters Chinese President Xi Jinping shakes trump's hand during a dinner at the start of a summit at the president's Mar-a-Lago estate in April.

The administration plans to ask other Asian allies to “do more” during the trip, national security adviser H.R. McMaster told reporters Thursday.

Trump has repeatedly threatened a military response if North Korea’s nuclear prowess continues to grow, going as far in a September speech as claiming he would “totally destroy” the country. The president also signed an executive order expanding sanctions that same month.

Trump “will remind friend and foe alike that the United States stands ready to defend itself and our allies using the full range of our capabilities,” McMaster said.

But he did note the administration is willing to “be a little patient here for at least a few months to see what more we and others can do.”

How much the Chinese are prepared to do on Trump’s behalf is up for debate. While China ― one of North Korea’s few allies and trade partners ― has imposed United Nations Security Council sanctions, it has also asked Trump to “cool it” with the inflammatory rhetoric and urged a diplomatic approach instead.

No president has spent this much time in Asia on one trip since President George H.W. Bush in the early 1990s, Reuters said.