Egypt is closing its airspace to Qatari planes in a growing diplomatic row, with Saudi Arabia and Bahrain expected to do the same on Tuesday.
Several countries have cut ties with Qatar, accusing it of supporting terrorism in the Gulf region.
Qatari nationals in Bahrain, Saudi Arabia and the UAE have been given two weeks to leave.
Qatar denies backing militants and its foreign minister has called for “a dialogue of openness and honesty”.
Egypt said it was closing off its airspace to Qatar from 04:00 GMT on Tuesday “until further notice”.
Travel disruption is expected as the airport in Doha, Qatar’s capital, is a major hub for international flight connections.
Airlines affected will include Qatar Airways, Etihad Airways and Emirates.
How passengers are affected
Why this row has erupted
Flight tracking technology by the FlightRadar24 website shows the limited route being taken by Qatar Airways flights on Tuesday morning
When avoiding the massive neighbour to the west, Saudi Arabia, Qatari planes will inevitably have to take longer routes leading to longer flight times.
But Qatar’s Foreign Minister, Sheikh Mohammed Bin Abdulrahman al-Thani, told broadcaster Al Jazeera the country would “still have access to the world through international sea lanes and international airspace”.
An anonymous Somali official told AP news agency at least 15 Qatar Airways flights had used Somalia’s airspace on Monday, many more than on a normal day.