In a message broadcast on the BBC World Service, the Foreign Office said the longer the delay, the more difficult and dangerous any departure might become. Eighty to 100 British nationals are believed to be working in northern Albania, away from the serious troubles in the south, where security has worsened.
"All British nationals should tell the British Embassy in Tirana what they intend to do," the Foreign Office said. "At the moment, most commercial airlines and ferry companies are operating normally, but this may change."
It urged all British nationals to leave Albania "by the first available commercial means." The list of those in Albania included journalists, aid workers, businessmen and "one or two intrepid tourists".
The British charity Children in Distress, which operates a children's hospital in Saranda, southern Albania, said that it had withdrawn all British and Irish staff. The hospital now has no children left in its wards.
Albania's president, Sali Berisha, said yesterday that he had appointed a new prime minister. Bashkim Fino, an economist from the southern town of Gjirokaster and a member of the main opposition Socialist Party, replaces Aleksander Meksi, a member of the ruling Democratic Party, who resigned last month as the unrest erupted.
The appointment of a member of the Socialist Party to the premiership was seen as a concession to the opposition, although they have little or no influence over the highly-localised rebel groups in the south.
Mr Berisha told Italy that a new government would be formed within 24 hours, the Italian Foreign Ministry said.
The president, his ruling Democratic Party and nine opposition parties signed an accord at the weekend to establish a national unity government and hold early elections by June in an attempt to find a political solution to the insurrection.
Political parties in Tirana agreed on Monday to split cabinet posts evenly between the Democratic Party and the opposition. However, the two sides have been deadlocked on who gets the key portfolios, political sources said.
The country's armed unrest spread from the south yesterday, with residents of a major town north of Tirana saying insurgents there have raided a military base and carted away weapons and ammunition.
A man identifying himself as the mayor of Bajram Curri said in a telephone call that insurgents took "a lot" of arms and munitions from the base in the town, 135 miles north of the capital, in a morning raid.