A gunman opened fire with a shot gun in a skate shop at a crowded shopping mall near Baltimore, killing two store employees and wounding another person, then apparently killing himself.
Howard County police said they did not know the motive for the shooting at the large mall in Columbia, Maryland, 32 km west of Baltimore.
The names of the dead have not been released but police said the employees who were killed were a man and a woman in their 20s.
One person suffered a gunshot wound to the foot, and four other people were injured in the chaos, police said.
A spokeswoman at Howard County General Hospital said all the injured were in good condition.
At the time of the shooting, the mall was crowded with weekend shoppers, many of whom sheltered in place after hearing the shots or seeing people fleeing.
The shooting, happened at about 4.15pm Irish time at a skate shop called Zumiez on the mall's upper level just above the food court.
Police said they found the body of the suspected gunman at the store and he had apparently died by suicide.
"He still had a large amount of ammunition on and about him and because of concerns about explosives and any other weapons he might have we are approaching this with an abundance of caution," Howard County Police Chief Bill McMahon told reporters.
Howard County Executive Ken Ulman said police arrived within two minutes of the 911 emergency call, but it took hours for the police to clear the building of shoppers and employees.
"This took a long time because you can imagine how many rooms there are in the mall. How many back offices, bathrooms and dressing rooms and nooks and crannies in the mall."
Colin Reddy, who works at the mall, told CNN he heard about eight or nine shots in all.
"We thought it was construction because there's a lot of construction going on at the mall right now. Then I heard it again. Like 'boom, boom, boom'. And then everybody started running," he said.
Mr Reddy said he and the other employees closed the store's gate and waited in a back room for police to arrive.
Tonya Broughton of Silver Spring, Maryland, said she and a friend were getting facials when they noticed other shoppers running.
"It was panic. We just headed for the nearest store,Victoria's Secret," she said, adding that the store's employees herded everyone to the rear of the store.
"They were very, nice, keeping us calm. They told us we were safe," she said.
The attack in Columbia follows a shooting at a New Jersey mall in November in which a gunman fired at least six shots without hitting anyone, sparking a mass evacuation of the complex, then killing himself.
There also have been a spate of shootings in recent days at US schools and universities.
A student was shot dead yesterday at South Carolina State University in Orangeburg, and at Purdue University in Indiana a teacher's assistant was shot and killed on Tuesday.
In both incidents suspects have been charged with the crimes.
Local police issued a tweet:
Three people confirmed dead at Columbia Mall. Victims unknown at this time.— Howard County Police (@HCPDNews) January 25, 2014