China has agreed to buy 200 Boeing jets, with a potential for the order to rise to as many as 750 planes, United States President Donald Trump has said, adding that the planes would have GE Aerospace engines.

The deal “includes approximately 200 planes and a promise of up to 750 if they do a good job”, Trump told reporters on Air Force One on Friday. More details about the deal, such as which type of jets and when the order would be delivered, were not immediately available.

Neither the Chinese government nor Boeing issued statements confirming the purchase agreement, which would mark a significant breakthrough in a market that was once central to the US aerospace company’s long-term growth and from which the US planemaker was largely shut out, amid trade tensions between Beijing and Washington. Planemakers usually disclose large deals once they are formalised.

Boeing CEO Kelly Ortberg was among a large group of US CEOs who joined Trump during the president’s trip to Beijing, seeking to sell products and services to China.

It was not immediately clear how many of the 200 planes announced by Trump represented new business for Boeing versus aircraft already in its order backlog.

People familiar with China’s purchasing patterns said Beijing has previously bundled new orders with repeat announcements when unveiling trade packages tied to diplomatic visits by US and European leaders.

For China, such a big order would secure capacity to keep growing its aviation market, even as production of its home-grown COMAC C919 narrow-body falls short of ambitious targets.

It would also help Boeing narrow the gap with rival Airbus, which has pulled far ahead in China in recent years.

An estimate from aviation intelligence and advisory firm IBA put the value of the 200-aircraft order at roughly $17bn to $19bn, assuming 80 percent of the mix is made up of MAX jets.

“This number, however, could increase to $25bn if a larger proportion [about 40 percent] of the total order is announced for the widebody aircraft,” IBA’s Samuel Kenekueyero said.

The deal would be a much-needed win for Trump, whose aggressive tariffs and other trade policies have so far failed to make much of a dent in the large US trade deficit.

An order for more than 500 jets, if it materialises, would be the largest in aviation history, surpassing IndiGo’s 500-aircraft deal for Airbus narrowbodies, though China’s purchase would likely be split among its three major state-run carriers.

Order size below expectations

Shares of the US planemaker had dropped nearly 4 percent on Thursday after Trump told Fox News Channel China had agreed to buy 200 jets, well below analysts’ expectations. They were down about 2.6 percent on Friday, while GE Aerospace shares fell 2 percent.

Industry sources have said Boeing was originally in negotiations for at least 500 narrowbody jets tied to the Beijing summit, with dozens of widebody jets and potentially as many as 200 to follow at a later date.

Trump said Xi would pay a return visit to Washington in September, implying it may become the focal point of the next tranche of potential plane orders.

However, concerns about after-sales support have weighed on buying decisions, said Li Hanming, an independent expert on China’s aviation industry.

“The reason China isn’t buying is very simple: no one wants to buy something without guaranteed after-sales maintenance and support. Last May, the US was still threatening export restrictions on parts. If they impose parts embargoes like that, who would still dare to buy Boeing?”

Wendy Cutler, senior vice president, Asia Society Policy Institute, and former acting deputy US trade representative, told Al Jazeera in emailed comments that, “What we expected and haven’t seen thus far is not only Chinese confirmation of the jet purchases, but other Chinese mega-purchases as well, particularly in the agricultural and energy sectors.”

Both sides also did not agree to extend the trade truce, which expires in five months, she pointed out.

“All of these matters appear to still be in the works, so we may see further announcements in the coming days. If further economic deliverable announcements are not forthcoming, it’s fair to conclude that this summit meeting was heavy on atmospherics, but light on substance,” Cutler said.