Lawmakers and the Trump administration are upping the pressure on China as worries about North Korea's nuclear capabilities grow.

President Trump's summit with Chinese President Xi Jinping's at Mar-a-Lago later this week will present Trump with his first in-person opportunity to make progress on his stated goal of reining in North Korea. China is likely in the best position to accomplish that as it has long propped up the isolated nation.

The White House on Tuesday said Trump plans to press Xi on taking a tougher approach. 

"I can tell you that it is now urgent," a senior White House official said of North Korea during a briefing in advance of Xi's visit. "The clock has now run out and all options are on the table for us."

The meeting comes at a time when fears about North Korea's nuclear program are growing.

Satellite imagery in recent weeks has indicated that Pyongyang may be preparing for its sixth nuclear test, which would follow two nuclear tests and a flurry of missile tests over the last year.

"It keeps most of us up at night because of the immediate problem," Sen. John McCainJohn McCainSenate panel approves Trump's Air Force secretary pick Republicans considering broader change to Senate rules Trump raises pressure on North Korea MORE (R-Ariz.) told The Hill about North Korea, adding that Trump should give Xi "a clear warning that if they continue to prop up North Korea, we'll take action to restrain them and it will have serious consequences in our relationship, including the economic relationships."

Throughout the presidential campaign and into his presidency, Trump has focused on China as the key to controlling North Korea.

In an interview with the Financial Times published Sunday, Trump reiterated that view but added that he's prepared to act unilaterally should China not help.

"China has great influence over North Korea. And China will either decide to help us with North Korea, or they won't," Trump told the newspaper. "If they do, that will be very good for China, and if they don't, it won't be good for anyone."

"If China is not going to solve North Korea, we will," he added later. "That is all I am telling you."

Harry Kazianis, director of defense studies at the Center for the National Interest, said Trump's comments could be setting the stage for negotiations with China.

"What Trump is trying to do is set the bar high," Kazianis said. "By saying we're going to take action alone, that doesn't necessarily mean military action. That could mean in theory that we could talk to North Korea alone and cut the Chinese out. That could be placing those secondary sanctions and not telling the Chinese ahead of time. Or it could be some sort of military action, but the downside of military action is almost unthinkable."

Experts have said secondary sanctions, which would target Chinese companies and nationals who support North Korea, could effectively cripple North Korea's economy and were not tried in earnest by the Obama administration. In September, the Obama administration sanctioned a Chinese company and four Chinese nationals for ties to North Korea's nuclear program for the first time, but critics said the step was not enough.

China is hesitant to take any action that could cause North Korea to collapse, experts say, because of the potential that it would unleash a flood of refugees and let loose weapons of mass destruction. Further, the collapse could result in a unified Korea, a powerful country on China's doorstep that would likely be allied with the United States.

North Korea loomed large during a Senate Armed Services Committee hearing Tuesday with the commander of U.S. Strategic Command, the combatant command in charge of the U.S. nuclear arsenal.

Gen. John Hyten told the committee that North Korea is what he's "concerned about most nights."

"Every time there's a launch, Feb. 11, March the 5th this year, the whole network comes up. We bring the entire power of my command to bear on the problem," he said. "Those are very concerning moments to me. Because we're not sure, every time they launch, we're not sure if this is a threat missile or not."

Hyten said China will have to be involved in dealing with North Korea.

"Any solution to the North Korean problem has to involve China," he said. "I'm a military officer, not a State Department official or any economic expert. But I just look at the world, and it's hard for me to see a solution without China."

In the House, concern about North Korea was in the spotlight Monday as lawmakers debated and then overwhelmingly passed two North Korea resolutions.

"There is no magic road to dealing with the North Korea threat that does not go through Beijing," Rep. Brad Sherman (D-Calif.) said from the House floor in reference to Trump's comments to the Financial Times.