WASHINGTON — China may not have a seat at the table during President Donald Trump's upcoming nuclear summit with North Korean leader Kim Jong Un, but U.S. officials say they are preparing to counter the Chinese spies they expect to be all over Singapore next week seeking inside information on the talks.

Chinese espionage against the U.S. has become more pervasive than that of any other adversary, current and former U.S. intelligence officials tell NBC News, and the Singapore summit is the latest spy-vs.-spy battleground.

The Chinese, who have been known to bug everything from hotel keys to the gifts given to American visitors, are expected to deploy their increasingly sophisticated repertoire of intelligence gathering techniques, both human and electronic, in Singapore.

Areas of concern for the U.S. at the summit include:

U.S. officials are concerned China has recruited informants among the waiters and other staff in Singapore’s restaurants and bars, who are paid to eavesdrop on American customers and report back to their Chinese handlers.

Officials also expect electronic surveillance of the summit meeting sites. Americans will sweep for bugs in rooms at the Capella Hotel that could be used for side discussions, and could erect tents inside hotel meeting rooms to block any concealed cameras from viewing classified documents.

Chinese intelligence agencies have shown the ability to penetrate mobile phones even when they are off, and U.S. officials are now told to take their batteries out when they are concerned about eavesdropping, according to a U.S. intelligence official.

"Chinese intelligence collection could be amped up around the summit," said Jeremy Bash, an NBC News analyst who was chief of staff to CIA Director Leon Panetta. "They have prioritized surveillance in recent years and their technical prowess has really advanced."

For years, the Chinese have engaged in a massive effort to recruit human spies in the West, and can call on an army of skilled hackers to gather intelligence from the web.

But recently Chinese intelligence agencies have grown more creative and adept, U.S. officials say, posing an increasing threat to America’s secrets.

“China remains a particularly aggressive espionage actor and is using increasingly sophisticated technological platforms to carry out its objectives,” said Dean Boyd, a spokesman for the National Counterintelligence and Security Center, the DNI’s new counterintelligence agency.

According to three U.S. officials, in one recent case a top U.S. official working in China repeatedly had trouble with his hotel key card. He had to replace it several times at the front desk because it wouldn’t open his door.

He brought one of the key cards back to the U.S., where security officials found a microphone embedded inside, according to the U.S. officials.

The Chinese have placed listening and tracking devices in chips embedded in credit cards, key chains, jewelry, and even event credentials, the officials said, often with the intent of capturing secret conversations among American officials.

President Donald Trump and China's President Xi Jinping meet business leaders at the Great Hall of the People in Beijing on Nov. 9. Damir Sagolj / Reuters

In advance of Chinese President Xi Jinping’s 2017 meeting with Trump at Mar-a-Lago, Trump’s south Florida estate, White House officials received detailed briefings on how the Chinese would try to spy on them during the visit "in every possible way,” said an official who was part of the visit.

And U.S. officials “swept all of our phones afterward” to check if they were infiltrated by the Chinese, the official added.

Seven months later when Trump traveled to Beijing, White House officials were given more extensive briefings, according to officials who were on the trip, in which they were told to assume the Chinese would be tracking, taping and watching them the entire time they were in the country.

During the visit, the officials say the Chinese gave the U.S. delegation pins that the Americans called their friendship pins. But members of the delegation were not allowed to wear the pins into a secure area because security officials warned they likely had embedded listening devices.

The officials said their belongings were rifled through while they were not in their hotel rooms, as happened to U.S. officials during previous presidential trips to China. Some senior members of Trump’s delegation packed carry-on bags with anything they didn’t want the Chinese to see and took the bags wherever they went, including out to dinner in restaurants, according to officials.