LONDON (AP) — The Latest on severe weather in Europe (all times local):
London's mayor has issued a "very high" air pollution alert for the first time, as cold, windless weather allowed emissions across the whole of southeast England to build up over the weekend.
The London air monitoring team at King's College London said pollution in the capital was at "black," the highest level, meaning people should reduce physical exertion outdoors.
The rise in pollution was caused by a combination of traffic pollution and wood burning, it added. That combined with an import of pollution from the continent on Sunday.
Officials warned that many other places across Britain were also suffering from high levels of pollutants known as particulate matter, and the problem is expected to continue Tuesday.
Dutch ice skaters are ignoring warnings about thin ice and taking to canals and lakes across the country that have frozen over in a cold snap gripping the Netherlands.
Dutch media reported Monday that many people had to be hauled out of chilly waters after crashing through thin ice on Sunday.
One area that was considered safe was the Ryptsjerksterpolder, near the northern city of Leeuwarden, which was covered in a shallow layer of frozen water.
Drone footage showed people skating past a windmill next to the ice in a quintessentially Dutch landscape.
Authorities in Serbia say that a man has been found dead in the snow in the southeast as cold spell persisted in the Balkan country.
The 58-year-old man's body was discovered when neighbors notified authorities after noticing he had been missing for two days. The man was from the village of Strbovac, a remote hamlet that was cut off by the snow.
Several people have died in freezing temperatures since extreme winter weather gripped the country in early January.
Authorities also have been battling thick ice that has formed on the Danube in Serbia, blocking all river traffic and endangering rafts and boats parked by the river banks.
Hungary has sent over its ice-breakers to help clear the ice that is up to 4 meters (13 feet) thick.
Thick fog has caused numerous flight delays and cancellations at London Heathrow and other area airports.
Travelers were advised Monday to check their flight status before going to the airport after roughly 100 flights were cancelled and many more were delayed.
The Met Office forecasting service said visibility at Heathrow had been reduced to roughly 100 meters (110 yards), leading to an overall slowdown in operations.
It issued a severe weather warning for London and most of southern England as driving conditions were also hazardous and slippery.
Conditions at Gatwick, London City and Stansted airports were also difficult with limited visibility.
Rescue crews are considering whether to start using heavy equipment to speed up the search for 23 people still buried under the ruins of a central Italy hotel crushed by an avalanche.
Firefighter spokesman Luca Cari said emergency crews were working with an "operational hypothesis" that the tons of snow that plowed into the Hotel Rigopiano on Jan. 18 might not have reached all parts of the structure, and that there might still be survivors underneath.
But five days after the devastating snow slide, Cari said Monday that "we are fighting against time."
He said: "We know we need to work fast, but in relation to an environment that doesn't allow for fast intervention."
Meanwhile, questions are intensifying into whether the local government underestimated the threat facing the isolated hotel.
Four people have died over the weekend in Austria while skiing, snow-shoeing or sledding — an unusually high toll linked to winter sports in the country.
The Austria Press Agency says that two Czech nationals snow-shoeing in Salzburg's alpine region died Sunday after being buried in an avalanche while two others managed to free themselves.
State broadcaster ORF says the two other deaths occurred Saturday. It said Monday that a German man was killed after he hit a rock head first while sledding near the Swiss border, and an Austrian skier died after colliding with a snow-boarder on a slope near the Italian border.
The snowboarder was only slightly hurt.