RAPID CITY, S.D. (AP) — Officials are stressing safety at the Sturgis Motorcycle Rally in western South Dakota, where four bikers have died in a span of three days.

Motorcyclists from Minnesota and Indiana died in crashes on Sunday, one from Colorado died Monday and another from Michigan was killed Tuesday. The rally that draws hundreds of thousands of people to South Dakota's Black Hills each summer officially began Monday and runs through Sunday.

Four motorcycle deaths were recorded during rally week last year, according to the Highway Patrol. The most deaths in the past five years occurred in 2010, when nine people died.

Law officers say speed and alcohol use are top concerns. The eye-grabbing scenery and challenging roads of the Black Hills also can quickly turn a comfortable ride into a deadly one, Patrol Lt. Rick Miller told the Rapid City Journal.

"When you come to western South Dakota, you have roads that curve and ditches that drop off or a steep embankment," he said. "A lot of nice bikes are around, the scenery is nice. When you're driving with everyone around you, you've got to be careful and pay attention to what's going on."

The South Dakota Safety Council has a motorcycle safety booth on Main Street in downtown Sturgis for the first time this summer, said Christina Steele, a spokeswoman for the rally. Local and state law enforcement officials also have geared up to enforce temporary rally-week traffic signals, respond to crashes and other calls and maintain order.

"We enjoy the first few days. And then it's busy," Kevin Karley, head of the Highway Patrol's Rapid City division, told the Journal. "It's a long week for those troopers."