Luton Airport had to divert flights after soaring temperatures melted the surface of its runway.
The airport said it had discovered a defect in the surface which was being repaired, and apologised to passengers.
Travellers took to social media to bring attention to the problem.
"Quick heads up - have just closed the runway at Luton airport for at least an hour. We were just about to be pushed back and they stopped everything. Inbound flights are being diverted."
Luton Airport confirmed the problem in a statement.
It said: "Following today's high temperatures, a surface defect was identified on the runway. Engineers were called immediately to site and repair works are currently in progress to resume operations as soon as possible.
"We would like to apologise for the inconvenience caused."
Departing flights were also delayed as the work was carried out.
It reopened at 6.05pm on Monday after the repairs were completed.
Forecasters said that the surface of roads and facilities like runways could have higher surface temperatures than the actual air temperature.
On Tuesday the surface of some roads could reach as high as 60C (140F), with air temperatures in the shade possibly breaking the 40C barrier (104F).