At least 12 people died in car accidents during the Memorial Day weekend, making it the deadliest unofficial start of summer Minnesotans have seen since 1996, according to officials from the state's Department of Public Safety.
Nine of those deaths occurred on Saturday, officials said.
The State Patrol responded to 10 of the deaths and seven serious injuries over the weekend. All of the crashes are still under investigation, officials said.
At least two of the seven motorists who died were not wearing seat belts, officials said.
Five of those deaths occurred in Olmsted County. In one collision, a pickup truck slammed into a minivan, killing four people and critically injuring two. The driver of the pickup truck had been drinking. It's unclear if the driver or passengers of the second car were wearing seat belts.
"This wave of tragedy demonstrates the ongoing threats on our roads, ranging from impaired driving, to speeding and not paying attention," State Patrol Lt. Matt Langer said in a statement. "Summer is the deadliest time on the roads and this past weekend serves as a serious reminder to take the task of driving seriously."
In 2008, two people were killed on Minnesota roads during the Memorial Day weekend. In 1996, 13 people died and in 1972, 16 people were killed over the holiday weekend -- the highest on record.
A statewide primary seat belt law goes into effect on June 9. The primary offense means drivers and passengers in all seating positions must be buckled up or in the correct child restraint.
Meanwhile, a statewide "Click It or Ticket" seat belt enforcement effort continues through May 31.