Edinburgh's hoteliers are backing a campaign calling for direct flights between the city and China.

The Edinburgh Hotels Association is the second major sponsor of the Edinburgh-China Air-Link project, which was set up in 2015 by Marketing Edinburgh, Edinburgh Airport, and The City of Edinburgh Council.

The association represents more than 50 hotels in the city. It joins jewelers Laing Edinburgh as an official sponsor of the campaign that is looking for support from local businesses to strengthen Edinburgh Airport's commercial case when pitching the idea of a direct route to Chinese airlines.

Currently, London and Manchester are the only United Kingdom cities with direct flights to China. Scottish authorities have long lobbied for a direct link to China, which Marketing Edinburgh has described as Scottish aviation's "holy grail".

Former Scottish First Minister Alex Salmond said during his trade mission to China in 2011 that a direct route was a top priority. So far, no airline has come forward to offer such a service.

"The main goal is the economic impact it would have for the city and the country," said Fiona Hunter, Edinburgh-China Air-link project manager. "The whole of Scotland would see a benefit, and there is a successful past for new UK air routes."

The amount of money Chinese tourists spent in Northern England doubled to an estimated 138 million pounds ($181 million) after Chinese carrier Hainan Airlines launched its direct route between Beijing and Manchester in 2016. And 17 charter flights between Beijing and Birmingham during the summer of 2015 contributed an estimated 19 million pounds to that local economy.

"I think it would be fair to say, given that Edinburgh is the most popular destination with Chinese tourists in the UK after London, that a link would be a success," Hunter said.

According to Marketing Edinburgh, at least 32,000 Chinese tourists visited Edinburgh in 2016. The actual figure is likely to be far higher because international passenger surveys do not accurately account for group travel, Hunter said.

In 2016, 150,000 visitors to Edinburgh Castle – the fortress that dominates the city's skyline – listed their point of origin as China.

Hunter said industries other than tourism and hospitality would benefit from direct flights, including trade. For example, the UK exported 52-million-pounds-worth of salmon to China last year. The majority of the salmon came from Scotland, via an intermediary airport. A direct link would benefit such perishable exports' shelf life.

Business links between China and Edinburgh where strengthened last year when Chinese travel agency Ctrip acquired Edinburgh-based fare aggregator Skyscanner for 1.4 billion pounds.

While Edinburgh is an established destination among Chinese travelers, Hunter said airlines want to be sure aircraft will be full in both directions.

And she said political uncertainty surrounding the UK's pending exit from the European Union and a potential second referendum on Scottish independence loom large.

"We don't know if there will be another independence referendum, and if that and Brexit will have an impact on visas and freedom to travel around," Hunter said. "The political landscape is unstable for airlines at the moment."