About 100 foreign diplomats, from Brazil to Turkey, gathered at the Trump International Hotel this week to sip Trump-branded champagne, dine on sliders and hear a sales pitch about the U.S. president-elect's newest hotel.

The event for the diplomatic community, held one week after the election, was in the Lincoln Library, a junior ballroom with 16-foot ceilings and velvet drapes that is also available for rent.

Some attendees won raffle prizes – among them overnight stays at other Trump properties around the world – allowing them to become better acquainted with the business holdings of the new commander in chief.

"The place was packed," said Lynn Van Fleit, founder of the nonprofit Diplomacy Matters Institute, which organises programs for foreign diplomats and government officials. She said much of the discussion among Washington-based diplomats is over "how are we going to build ties with the new administration."

Back when many expected Trump to lose the election, speculation was rife that business would suffer at the hotels, condos and golf courses bearing his name. Now, those venues offer the prospect of something else: a chance to curry favour or access with the next president.

Perhaps nowhere is that possibility more obvious than Trump's newly renovated hotel a few blocks from the White House, on Pennsylvania Avenue. Rooms sold out quickly for the inauguration, many for five-night minimums priced at five times the normal rate, according to the hotel's manager.

To many of the guests at the reception Tuesday, accepting an invitation to tour the $212 million hotel and check out the $20,000-a-night, 6,300-square-foot "town house" suite seemed like a good idea. They spoke admiringly about the renovation and left with a goody bag of chocolates and a brochure. It listed the choices of accommodations and meeting rooms, and expounded on the location's "striking prominence" at historical moments such as the Inauguration Day parade.

"Believe me, all the delegations will go there," said one Middle Eastern diplomat who recently toured the hotel and booked an overseas visitor. The diplomat said many stayed away from the hotel before the election for fear of a "Clinton backlash," but now it's the place to be seen.

In interviews with a dozen diplomats, many of whom declined to be named because they were not authorised to speak about anything related to the new U.S. president, some said spending money at Trump's hotel is an easy, friendly gesture to the new president.

"Why wouldn't I stay at his hotel blocks from the White House, so I can tell the new president, 'I love your new hotel!' Isn't it rude to come to his city and say, 'I am staying at your competitor?' " said one Asian diplomat.

Guests at the Trump hotel have begun parking themselves in the lobby, ordering expensive cocktails, hoping to see one of the Trump family members or the latest Cabinet pick. One foreign official hoped Trump, famous for the personal interest he takes in his businesses, might check the guest logs himself.

But several expressed concern that spending thousands of dollars on a Trump property could look like an attempt to buy access or favours.

"The temptation and the inclination will certainly be there," said Arturo Sarukhan, a former Mexican ambassador to the United States. "Some might think it's the right way to engage, to be able to tell the next president, 'Oh, I stayed at your hotel.' If I were still in government I would discourage it, among other reasons because it can be questioned and looked at in a very poor light, as though you are trying to buy influence via a hotel bill."

If diplomats, as well as corporate representatives and executives – whom the hotel hosted in a separate room Tuesday – want to spend lavishly at Trump properties, there appears to be no ethics rule to stop it, short of an act of Congress.

The Trumps opened the hotel in the Old Post Office pavilion, a 117-year-old property the company leases from the federal government. Officials at the General Services Administration, the landlord, have consulted the Office of Government Ethics about how to handle such conflicts, but the measures preventing other federal employees from profiting from their positions do not apply to the president.

"Consequently, there is no current legal requirement that would compel the President to relinquish financial interests because of a conflict of interest," an analysis produced last month by the Congressional Research Service at the Library of Congress said.

Foreign leaders and top officials visiting Washington often stay at Blair House or in their ambassador's residence, but many are accompanied by entourages who take over entire floors of hotels. The 180-country-strong diplomatic community in the capital spends millions of dollars every year on hotels, including for huge events marking their countries' independence days.

Foreign business is so critical to Washington hotels that the Trumps, like others, hired a "director of diplomatic sales," luring the manager from a top competitor, the Four Seasons in Georgetown.

The hotel's general manager, Mickael Damelincourt, said in an interview business had been picking up before the election and interest had surged for the inauguration. Hotels throughout the city, as well as Airbnb users, are charging higher rates because of increased demand.

"I got 50 calls in the last day, from some very important people, and we have no space," Damelincourt said.

He said he didn't think inauguration guests were coming to his hotel in order to curry favour with the president-elect. "I don't think that has an effect on the hotel," he said.

"I think we would be doing amazing business anyway because of our location and because of the quality. Look at the W hotel, they are doing amazing, as well."

Trump has said he will turn over his businesses, including hotels and golf courses around the world, to his children Donald Jr, Ivanka and Eric.

"This is a top priority at the Organization and the structure that is ultimately selected will comply with all applicable rules and regulations," including at the Old Post Office, the Trump Organization said.

Several top ethics experts, including former White House counsels, say handing the properties to the Trump children will not go nearly far enough in quashing concerns Trump could use the presidency to enrich himself or his family.

More than a dozen watchdog organisations penned a letter to Trump on Thursday, urging him to create a true blind trust or liquidate the assets. (Under a blind trust an independent trustee with no familial ties would manage the properties.)

"Failure to follow this course of action will create conflicts of interest of unprecedented magnitude," groups including Common Cause wrote.

Democratic representative Katherine Clark, introduced a bill this week that would require presidents to take similar steps.

F. Joseph Warin, a lawyer and expert on the Foreign Corrupt Practices Act, said Trump should consider bringing in a third-party administrator.

"It's about perception of conflict of interest," Warin said. "We want our leader laser-focused on fixing the problems of the United States and not diverted on commercial issues."