Around 1,500 passengers expecting to arrive at Gatwick airport were diverted elsewhere overnight after their aircraft were unable to land.
The airport blamed poor visibility and urgent runway maintenance work.
A total of 24 flights had to be diverted to Stansted, Luton and Bristol airports and travellers had to take coaches back to Gatwick.
The airport it hoped services would have returned to normal this morning.
Engineers were carrying out planned maintenance work to the airport’s main runway overnight, leaving just the second landing strip open.
But fog meant short and medium-haul flights had to be diverted from around 12.10am onwards.
A Gatwick spokesman said: “We had some planned runway maintenance works scheduled for last night which all flight operators were informed about and when we do that we have to use our second runway which is a visual strip.
“We then suffered some fog which led to 24 aircraft being diverted.”
EasyJet, British Airways and Thomson Airways passengers were affected by the disruption.
Three BA short-haul flights due to depart from Gatwick this morning have been cancelled because of the disruption and eight flights have been delayed.
London City Airport was also suffering fog problems this morning.
“Due to low visibility this morning, flights are experiencing disruptions. Passengers are advised to contact their airlines for more information,” a spokesman said.