The Foreign and Commonwealth Office (FCO) has advised British people against all non-essential international travel, initially for 30 days.
The advice is effective immediately.
The FCO said whether travel is considered essential or not is a personal decision.
“It is for individuals themselves to make an informed decision based on the risks and FCO advice. Anyone still planning to travel should check the validity of their travel insurance,” it said.
It is not currently advising British people to immediately return to the UK if they are overseas, except for a few countries (visit gov.uk for specific advice).
But it said people should keep in mind that flights may be cancelled at short notice, and other travel restrictions may be put in place by foreign governments.
“This change in travel advice reflects the pace at which other countries are either closing their borders or implementing restrictive measures in response to the global coronavirus pandemic,” the FCO said.
“Often there is little or no notice when countries take these steps and restrictions are also being imposed in areas where no cases of coronavirus have yet been reported. They are therefore very difficult to predict.
“British people who decide that they still need to travel abroad should be fully aware of the increased risks of doing so.
“That includes the risk that they may not be able to get home, if travel restrictions are put in place. Anyone still considering travel to be realistic about the level of disruption they are willing and able to endure, and to make decisions in light of the unprecedented conditions we face.”
It said that 430 changes have been made to FCO Travel Advice in the last week.
It added: “We will continue to do everything in our power to get those British nationals affected the care, support and advice they need.
“We are also working urgently to ensure international governments have sensible plans to enable the return of British and other travellers and, crucially, that they keep borders open for enough time to allow people to return home on commercial flights.”
Most airlines have announced capacity reductions of 70 to 90 per cent for the coming months.