The Foreign Office has warned Britons against travelling to Bangkok after violence and rioting erupted in the Thai capital.
Soldiers and tanks appeared in the city after the Thai authorities declared a state of emergency - a day after protests stopped a major Asian summit.
The FCO urged anyone considering a trip to the capital or its surrounding areas to "urgently review their plans".
It estimates that 40,000 British nationals live in Thailand.
Advice on the FCO website read: "In view of the deteriorating security situation anyone considering going to Bangkok should urgently review their plans.
Stay indoors
"British residents in, and visitors to, Bangkok are advised to avoid any areas where demonstrations are taking place and to stay indoors as far as possible."
It said there were 15 staff members on duty to deal with the situation at the embassy, but no British tourists had reported any incidents so far.
Protesters have blocked a number of busy road junctions and at least one railway, and taken buses and two armoured vehicles.
The prime minister has threatened "tough measures" to end the protests.
But the army has so far not moved against the crowds. Hospitals have been asked to prepare for casualties in case they do.
BBC NEWS | UK | FO issues Bangkok travel warning
Cue all the cancellations of holidays and flights.