All sides must refrain from violence in an effort to secure a "stable and successful" Zimbabwe, Boris Johnson said after a military takeover in Harare.
The Foreign Secretary said the situation was "fluid" and the UK's ambassador to the African country said the military remained on the streets at key strategic locations in the capital.
Zimbabwe's dictator Robert Mugabe is "fine" but confined to his home after a night of unrest that included a military takeover of the state broadcaster, South African president Jacob Zuma has said.
Mr Johnson, who will update MPs later, said: "We're monitoring the situation very closely as you can imagine, and our ambassador has been in touch to say that obviously our UK nationals are worried, they should get in touch with our embassy.
"At the moment it's very fluid and it's hard to say exactly how this will turn out. I think the most important point to make is that everybody wants to see a stable and successful Zimbabwe.
"I think we are really appealing for everybody to refrain from violence. That's the crucial thing."
The UK's acting ambassador to Zimbabwe Simon Thomas said: "I can confirm that military remain deployed at strategic locations around Harare this morning.
"As an embassy our prime concern is obviously for the safety and security of British nationals and our advice to any British nationals who are here in Harare, either living or working or visiting, is to stay at home, stay in your hotel room, wait until things settle down a little bit."