Bands of so-called "war veterans" in Zimbabwe have been storming foreign-owned businesses in the country, extorting money and beating staff.
Foreign Office Minister Brian Wilson said the local police force had not intervened in what he described as a "deeply worrying development".
Advising UK nationals to contact the British High Commissioner in the country, he said that there had not been any reports of serious injuries.
The Government would continue to monitor the situation overnight very closely, he said, and would consider what action was necessary tomorrow morning.
Liberal Democrat foreign affairs spokesman Menzies Campbell urged the Government to take a "generous attitude" to people fleeing the country and seeking asylum in Britain.
Mr Wilson said he did not wish to inflame the situation by making such promises and repeated the advice to nationals to contact the British Consulate for advice.