"Due to a recent outbreak of Covid affecting staff in Hanoi, it was necessary to close the U.K. visa application center," it said on its official Facebook page.
Additional appointments will be available over the coming weeks for those affected by the recent closure.
Hanoi has topped the country’s daily infection tally since December, with cases climbing to over 10,000 a day.
It has recorded over 285,000 cases and 1,000 deaths during the fourth wave that began last April.
The outbreak could peak in two more weeks, city chairman Chu Ngoc Anh said.
Some 12,000 Vietnamese students are studying in the U.K., according to official statistics.