The city’s tourism numbers are expected to take a major hit thanks to President Donald Trump’s proposed travel ban, and the economic impact could be devastating, officials said at a City Council hearing on Thursday.

The official tourism arm is hoping to counter Trump’s “hostile ‘America First’ rhetoric” with a multimillion-dollar ad campaign aimed at countries that often send the most U.S. visitors, including the United Kingdom, Germany, Mexico and Spain, the agency’s research chief said at the hearing.

The $3 million multi-language campaign, called “ALL ARE WELCOME,” is set to debut in the coming weeks, said officials from NYC & Company. Ads promoting the campaign will be featured on street banners, bus stops and other spots that prospective tourists might see.

“The message is being sent that walls are going up and doors are closed. That’s not the message we want to be sending in New York City,” said City Councilman Dan Garodnick, who chairs the Council’s Economic Development Committee, which held the nearly two-hour hearing on Thursday.

The city is projecting 300,000 fewer foreign tourists in 2017 compared to last year — and 700,000 fewer than projected — and New York stands to lose more than $1 billion in revenue. Business travelers and foreign-born New York employee numbers have also declined, according to experts who testified at the Council hearing.

Matt Chaban, a policy director for the Center for an Urban Future, said foreign-born New Yorkers represent a major component of several job sectors and contribute $257 billion in economic activity.

City immigrants make up 70 percent of medical and life science jobs, 60 percent of civil engineers and 59 percent of pharmacists, according to Chaban.

“Immigrants create massive economic dividends, not only for themselves but for their entire communities,” he said.

Councilman Joe Borelli (R-Staten Island), one of only three non-Democrats in the 51-member Council and a Trump supporter, questioned whether other factors, such as financial regulation or hotel-building restrictions in the city might impact the economy and tourism, rather than Trump.

Donna Keren, NYC & Company’s senior vice president for research and analysis, countered that the tourist arm’s forecast models — currently based on internet searches and flight bookings that dip when, for instance, Trump announced his executive orders — have been proved right time and again since 2003.

As part of the promotional campaign, city tourism experts will work with travel agents, travel magazines and other media players to help sell the message that New York is welcome to all, according to Keren.

“The idea is we catch people’s eye and then back it up through all of these other channels,” she said. “We’re standing on solid ground. New York is the most popular international destination in the country for a reason.”