A midmorning snow squall Thursday spawned a 29-­vehicle pileup on westbound Interstate 94 near Monticello that included 15 semitrailer trucks and at least one that burst into flames.

Heavy black smoke billowed into the air for hours after the crash near milepost 194, the exit for County Road 39, forcing authorities to shut down the westbound I-94 lanes around 9:15 a.m.

The eastbound lanes were later closed to allow room for crews to extinguish fires that had spread from a truck carrying tractor tires to nearby vehicles. The eastbound lanes reopened just after 1 p.m., and the westbound lanes reopened by early evening.

Nine people were transported by ambulance for what appeared to be minor injures, according to a statement from the Minnesota State Patrol.

A backhoe was brought in to help remove burned vehicles, tires and other debris.

Images from MnDOT traffic management cameras showed dozens of mangled vehicles, with some pinned up against a concrete median. Some semitrailer trucks had their sides ripped off, exposing their contents, while others straddled both westbound lanes.

Another semitrailer truck jackknifed near Wright County Road 19, and the State Patrol said it was responding to crashes in the area Thursday morning.

The crashes occurred during a snow squall that passed through Wright County and into northwest Hennepin County. Motorists were advised to avoid or delay travel until the squall passed, the National Weather Service said.

The Weather Service's Grand Forks office tweeted that snow squalls are "dangerous intense bursts of snow that can drop visibilities quickly to whiteout and typically will last 30-60 minutes."

The State Patrol asks anyone with information about the incident to call 1-320-223-6666.

The quick-moving burst dropped 2.5 inches of snow in Buffalo, about 10 miles south of Monticello. Other totals included 1.6 inches in Mounds View, 1.4 inches in Bloomington, 1.3 inches in Chanhassen and eight-tenths of an inch in Minneapolis, the Weather Service said.

Tim Harlow • 612-673-7768