Owing to technical problems, Visa credit card transactions across Europe were being declined.
"We are currently experiencing some technical problems in our card transaction processing," London-based Visa International said in a statement. "In some cases, this is resulting in card transactions being declined."
Payment Business Services, a Danish company that handles credit cards transactions, said in Copenhagen that it began noticing technical problems with Visa transactions shortly before 5 a.m. (0300GMT), with Visa transactions being rejected two hours later.
Visa International said it first noticed problems in Britain midmorning. The company said it did not have a figure for the total number of transactions affected.
"Immediate action is being taken to overcome this problem and we hope to have a full service resumed as soon as possible," the statement said.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969