Police say it was believed to be "a domestic-type incident"
Two people have been shot dead at Central Michigan University and police are still searching for the gunman.
The US university said the shooting began on the fourth floor of Campbell Hall at around 8.30am local time.
The two people killed were not students or staff, police said.
There were no other injuries.
CMU Police Lieutenant Larry Klaus said the campus was "on active lockdown and students are sheltering in place".
He said police had contacted the suspect, James Eric Davis Jr, the previous evening and that he had been taken to hospital "due to what police believe might have been a drug-type incident - an overdose or bad reaction to drugs".
He would not give any details on a possible motive or the suspect's relationship to the victims, saying only that it was believed to be "a domestic-type incident".
He also did not reveal the type of weapons used.
The suspect was described as a black 19-year-old, 5ft 10in tall, and wearing yellow jeans and a blue hoodie.
Officers have been scouring the campus on foot while helicopters search from above.
Jeff Browne, Mount Pleasant Police public information officer, said anyone who sees Davis should not approach him and instead call 911 immediately.
He added: "The important thing is to know our community is safe (but we) ask that everybody stay inside at this time."
Halie Byron (20) locked herself in her house, about 10 minutes' walk from Campbell Hall.
She said: "It's scary thinking about how easy a shooter can come into a college campus anywhere - a classroom, a library.
"There's so much easy access."
Parents hoping to collect their children for spring break were told to go to a local hotel instead.
Central Michigan University has about 23,000 students in Mount Pleasant, about 70 miles north of Lansing, the state's capital.
The shooting comes two weeks after 17 people were shot dead at a Florida high school, sparking a renewed debate over gun violence in the US.