Emirates and Boeing were poised on Wednesday to seal a compromise deal that would see the Dubai carrier order around 30 787 Dreamliners, paving the way for a reduced order for delayed 777X jets, people familiar with the matter said.

Emirates tentatively ordered 40 Dreamliners in 2017 but "tough" last-minute talks to finalise the order this week have hinged on negotiations over the fate of a massive separate order for 150 777X after the latter ran into delays, they said.

A restructuring of the 777X order may, however, not be highlighted officially at the Dubai Airshow, where Emirates plans an announcement for 7am (GMT) on Wednesday.

Emirates and Boeing declined to comment.

Sources cautioned talks were still going on in Dubai and the number of aircraft ordered could be subject to last-minute adjustments, but said it was unlikely Emirates would take all 40 787 jets announced at the largest Middle East air show in 2017.

One source said the order could involve as many as 35 787s.

Emirates has been looking at reducing part of its 777X order, which the airline's president Tim Clark said on Tuesday could be influenced by the delays and, in turn, determine whether it went ahead with a 787 deal.

Emirates says it no longer knows when it will receive its first 777X, which was supposed to be delivered next year. Boeing has said the 777X will be delivered in 2021.

Easing an eight-month-old crisis over the grounding of its smaller 737 MAX, Boeing had earlier at the November 17-21 show won tentative or firm orders for 60 of the grounded MAX jets.

But industry sources had warned that Boeing had risked leaving Dubai without resolving the critical set of interlocking deals with Emirates, the industry's largest customer for wide-body jets and the backbone for the 777X programme.

A high-profile order announcement on Wednesday would also effectively deliver a message of support from Dubai for the troubled United States planemaker, whose ongoing MAX crisis has harmed Emirates sister carrier flydubai, analysts said.

The United Arab Emirates, which includes Dubai, is a close ally of the US, which has poured support into the region amid tensions between Iran and Gulf Arab states that provided a tense backdrop to the Middle East industry event.