No public buses were operating in the city of Braganca, located some 500 kilometres (300 miles) northeast of Lisbon, because of the wintry conditions, the deputy mayor of the city, Rui Caseiro, said.

"Roads looks like mirrors," he told the Lusa news agency.

Snow began to blanket the region on Sunday, forcing the closure for several hours of the IP4 highway which links northern Portugal to Spain.

Officials said they expected the situation to improve throughout the day as ploughs managed to clear roads and temperatures rose, helping to melt the ice and snow.

The national weather office expects temperatures in Braganca, which dipped to minus 1 degree Celsius (30 degrees Fahrenheit) overnight, will reach a high of 5 degrees Celsius on Monday.