A quickly accumulating snowfall walloped Twin Cities motorists and mass-transit commuters Thursday morning, spawning countless crashes that caused significant delays and triggered snow emergencies in Minneapolis, St. Paul and several suburbs.

The scene on southbound Interstate 35 at Hwy. 8 in Forest Lake resembled a demolition derby for a time. Highway cameras showed scores of crashed vehicles.

Difficulties persisted into the afternoon, even after the snow stopped. A three-vehicle crash occurred about 1:10 p.m. inside the Lowry Hill tunnel along westbound I-94 in downtown Minneapolis. There was another multivehicle pileup at about the same time on westbound I-94 near Riverside Avenue.

The National Weather Service (NWS) reported 6.7 inches in Plymouth, 6.3 at the Minneapolis-St. Paul International Airport, 6 inches in north Minneapolis and downtown, 5.5 inches in Northfield, 5.3 in North St. Paul, 5.2 in Fridley, 4.7 in Watertown and 4.6 in Owatonna.

Minneapolis and St. Paul each declared a snow emergency, which took effect at 9 p.m. Thursday.

Suburbs such as Plymouth, Bloomington, Eden Prairie, Golden Valley and Robbinsdale did the same.

A full armada of plows could not keep up with snow that fell at an inch-an-hour during the morning rush, and that irritated motorists. Scores lodged complaints, said Bobbie Dahlke, a MnDOT spokeswoman.

All through the morning, Metro Transit buses ran well behind schedule, at times two-thirds of them or more, with delays averaging up 25 minutes.

Diving temperatures will be the challenge on Friday — they were predicted to drop sharply into the evening Thursday and tumble to minus 9 overnight. Windchill readings could hit 30 below before dawn Friday, according to the NWS.