The University of Wisconsin-Madison has asked students to "shelter in place" on Wednesday evening following a report of shots being fired near the campus, according to an alert posted on the university's website.
The university said in the alert that police were searching for a suspect last seen heading toward university residence halls.
The Senate Democratic Leader Harry Reid has accused the NRA and gun lobby of "shameful scare tactics", after an amendment which would have expanded background checks on people wanting to buy guns, failed to secure enough of the vote to be put into law.
Opponents of the measure say that said the proposals were an example of government overreach that would infringe on the constitutional right to bear arms.
We must strike a better balance between the right to defend ourselves and the right of every child in America to grow up safe from gun violence.
If tragedy strikes again if innocents are gunned down in a classroom or a theatre or a restaurant I could not live with myself as a father, as a husband, as a grandfather or as a friend knowing that I didn't do everything in my power to prevent.
The US Senate has cleared the way for what are likely to be heated debates about gun-control legislation, avoiding a Republican-sponsored effort to block the talks.
Senators voted 68-31 to open debate on President Barack Obama's proposals to expand background checks for gun buyers, tighten restrictions on gun trafficking and increase funding for school security.
The issue of gun-control exploded onto the political agenda in the wake of the Newtown massacre last December in which 20 children and six adults were shot dead at an elementary school.
The legislation still faces many hurdles and weeks of discussion in both the Senate and House of Representatives.
A six-year-old boy in New Jersey has died after being shot by a friend, aged just four, as their parents stood nearby.
Toms River police chief Michael Mastronardy said: "The six-year-old ... retrieved a rifle within the house, a .22-caliber rifle, came outside...
“A shot went out and the six-year-old was struck in the head."
The incident followed another fatal shooting days ago, this time in Tennessee, that also involved a four-year-old boy.
US President Barack Obama has reiterated his call for "commonsense measures" to reduce gun violence
Speaking on Gun Appreciation, he said that his Administration is taking 23 measures under its existing authority, but that Congress must join him in passing legislation to ensure a lasting impact.
President Obama has said he is in favour of a universal background check for anyone trying to buy a gun, and a ban on military-style assault weapons.
President Barack Obama has said that he has a "list of sensible, common-sense steps" to ensure that another school shooting does not happen in the US.
He said his starting point had not been what was politically possible, but "what makes sense".
"We're going to have to come up with answers that set politics aside, and that is what I expect Congress to do," he added.
He did not go into detail about what the proposals would look like, but mentioned stronger background checks and restrictions on the sale of high capacity magazines and assault weapons.
The police chief of the American town where a gunman opened fire in a primary school killing 20 children last December has joined the calls for stricter gun controls.
He said that the gunman, who attacked Sandy Hook Elementary School in Newtown, Connecticut, was better armed than the police that were trying to stop him.
"We never like to think we’re going to be outgunned in any situation we’re dealing with."
He also said that criminal background checks on people buying guns needed to be improved.
This is the first in a series of meetings that President Obama promised in the wake of the shooting to deaths of 26 people at a primary school in Newtown, Connecticut last December.
As well as pro-gun groups, Vice President Biden is due to meet victims’ groups, gun-safety advocates and representatives from the video game and entertainment industries, according to NBC News.