By Tim Hepher and Alexander Cornwell

DUBAI Middle East carriers look set to order tens of billions of dollars of long-haul jets at the opening of the Dubai Airshow on Monday, as Emirates renews confidence in the delayed Boeing 777X while facing new competition from rivals like Turkish Airlines.

Hosts Emirates and low-cost cousin flyDubai are expected to stamp their mark early on the world's second-largest aerospace event, industry sources said, despite concerns about a drop in the economically key travel sector due to Mideast tensions.

That's likely to include an order for several dozen Boeing 777X jets, despite ongoing uncertainty over the schedule for the world's largest twin-engined jet, currently expected in 2025 after a five-year delay. Boeing has said the schedule is intact.

The world's largest user of wide-body jets, including Airbus A380 superjumbos and current-generation Boeing 777s, has publicly said it is considering the upgraded 777X model as well as the Airbus A350 and smaller Boeing 787 for a new batch.

Of these, the 787 is least likely to feature immediately.

FlyDubai flies Boeing 737 MAX narrowbody jets and is set to order more planes in that category, sources said.

Emirates, Airbus and Boeing declined comment.

Industry officials estimate airlines worldwide are negotiating behind the scenes to buy some 700-800 new jets, including 200-300 of the world's largest, as they catch up on fleet replacement plans set aside during the pandemic.

How many of those bear fruit in time for the Nov. 13-17 show depends on the state of negotiations and jockeying for the limelight as Gulf groups face a widening circle of competition.

Turkish Airlines (THY) burst onto the show's agenda on Saturday with word from state-run Anadolu news agency that it was in talks to buy up to 355 Airbus jets.

Following more talks, industry sources said the airline could announce at least part of the deal on Monday.

It has said it is in discussions for as many as 600 planes overall, likely to be split between Airbus and Boeing.

One Mideast source described the prospect of a Turkish order as a "bold move," stepping up competition at the showcase event.

However, speculation of a large Dubai order for narrowbody jets from the region's newest player, Saudi Arabia's Riyadh Air, as early as Dubai is premature, other sources said.

The airline, which has hinted at a decision in coming weeks, declined to comment.

Aviation powerhouse Dubai is staging the biennial aerospace pageant against the backdrop of the Israel-Hamas war in Gaza that is pushing up demand for weapons and closing airspace, making flights longer and more expensive for some airlines.

Travel analysis firm ForwardKeys said on Friday flight bookings had fallen not only in the Middle East, but around the world since Oct 7. Bookings to the Middle East have slumped 26%, it said.

(Reporting by Tim Hepher, Alexander Cornwell; Editing by Hugh Lawson)