The Foreign and Commonwealth Office is advising against all but essential travel to mainland Spain. Quarantine measures apply to those returning from mainland Spain, the Canary Islands and the Balearic Islands, such as Majorca and Ibiza.
British Airways is still operating flights, but said the move was "throwing thousands of Britons' travel plans into chaos".
Yesterday the UK's biggest tour operator, Tui, cancelled all mainland Spanish holidays until 9 August.
Today Ryanair posted a loss and expressed concern about a possible second wave of coronavirus in the Autumn.
The company said: “It is impossible to predict how long the Covid-19 pandemic will persist, and a second wave of Covid-19 cases across Europe in late autumn (when the annual flu season commences) is our biggest fear right now.
“Hopefully EU governments, by implementing effective track and tracing systems, and EU citizens by complying with recommended face masks, rigorous hand hygiene and other measures, will avoid the need for further lockdowns or restrictions on intra-EU flights.”
Shares in British Airways owner IAG tumbled 8%, while was EasyJet was off 12% and Wizz Air dived 5%.
InterContinental Hotels Group was down 3% and Tui lost 13%.
Joshua Mahony, market analyst at IG, said: “The airlines have led the loses in early trade today, with the likes of TUI, IAG, Dart Group, EasyJet, and Ryanair all suffering after the swift UK decision to reimpose a 14-day quarantine on any flights from Spain.
"Whilst some will criticise the speed at which these measures have been imposed, it does show a willingness to act early in a bid to reduce imported cases in the UK.
"With Ryanair losing €185m over the April-June period, airlines desperately need a smooth summer as they bid to stabilise their balance sheet after months of losses.
"Unfortunately, this Spanish quarantine announcement is unlikely to be the last of its kind, with outbreaks throughout Europe likely to provide a stop-start summer for airlines as different regions attempt to extinguish any surges in Covid-19."
