(CNN) -- A blast of harsh winter weather socked Europe on Saturday morning, causing travel chaos and sending temperatures into a deep-freeze ahead of a busy holiday travel week.
From Northern Ireland to Bulgaria, blizzard conditions left airports with heavy delays or shut them entirely on Friday, and many delays and cancellations continued into Saturday.
London's Heathrow and Gatwick airports closed all runways Saturday afternoon because of heavy snow and ice, though Gatwick reopened at 3 p.m. after clearing 4 inches of snow from the tarmac. Despite the reopening, the airport warned of "inevitable" delays and cancellations throughout the day.
British Airways canceled all Saturday domestic and European flights at Heathrow, and all long-haul flights due to depart before 7 p.m. were also grounded. All easyJet and British Airways flights -- with the exception of a flight to Egypt -- were canceled out of Gatwick as well.
Police closed several access roads surrounding the airports due to dangerous driving conditions.
The delays and cancellations extended across Europe -- to Amsterdam, the Netherlands; Geneva, Switzerland; Munich, Germany; Paris, France; and Copenhagen, Denmark.
Heavy snowfall also forced the closing of Hungary's Budapest Ferihegy International Airport on Saturday. It had reopened by 4:30 p.m.
Ireland braced for an icey Saturday as the Irish Meteorological Service, Met Eireann, forecast widespread frost, ice and freezing fog for the morning, and some sleet and snow showers for later in the day. Temperatures were expected to drop down to between 4 and 8 degrees Celsius below zero (between 18 degrees and 25 degrees Fahrenheit) Saturday night.
Northern Ireland was blanketed at the end of this week with its worst snowfall in 25 years, according to CNN affiliate TV3.
The government issued emergency snow warnings Friday night, and more snow was expected Saturday.
The Police Service of Northern Ireland warned motorists to avoid treacherous roads and travel "only if absolutely necessary."
At Frankfurt Airport Saturday morning, snow was still coming down.
"We have a light snow now. According to the weather forecast, the snowfall should stop in three hours," airport spokesman Tino Ross said. Approximately 240 flights were canceled Saturday and there were still some delays, according to airport officials.
Airport personnel were working Saturday morning to de-ice airplanes and resume full operations at the airport, Ross said. He added that while about 3,000 passengers were stranded Friday, after having passed through passport control, the situation has improved Saturday and that stranded passengers were provided food and water for the wait.
The relentless weather caused approximately 250 flights to be cancelled and thousands of passengers stranded at Amsterdam's Schiphol airport on Friday, according to airport spokeswoman Antoinette Spaans.
"We are expecting more delays due to weather conditions," Spaans said Saturday. "The most delays and cancellations are expected to affect air traffic within Europe," she added.
To the south in Bulgaria, the eastern part of the country has been under snow for three days, with accumulation at nearly 1 meter (40 inches) in some areas, according to CNN affiliate bTV.
The main highway, airport and port in Varna, Bulgaria, were closed Friday for several hours. Four regions in Bulgaria -- Silistra, Dorbich, Varna and Burgas -- elevated the weather advisory, and the country was still expecting heavy snowfall and strong winds, bTV's website said. Many roads remain closed, and town and villages were without water or electricity.
In Belgium, the weather forced truck drivers to spend a freezing night in their cabs after authorities banned trucks over seven tons from travelling on icy roads.
Italy's ANSA news agency reported that two people had died because of the bad weather -- a truck driver who was killed in a car accident and a man who died of a heart attack while cleaning up snow outside his house. Hundreds of passengers were stranded in Florence, Italy, after snow and ice stopped high-speed trains from entering the city's train station, the agency said.
In northeastern Greece near Macedonia, heavy snowfall mid-week caused massive problems on several highways, where snowchains were declared mandatory, according to national news Athens News Agency.
Meteorologists say the cold weather is caused by a negative phase of the Arctic Oscillation, which means that cold Arctic air is flowing into southern latitudes that are normally much warmer.
Forecasters don't expect conditions to change anytime soon. The next wave of snowy weather is expected to bring up to 20 centimeters (8 inches) to some parts of the U.K., with London expected to receive 5 to 10 centimeters (2 to 4 inches) of snow.
The weather system will move across France and Germany on Saturday night and Sunday. Below-normal temperatures are expected to continue in northern Europe into the beginning of next week.
