Twenty children and six women died in Friday's assault on Sandy Hook school in Newtown by a lone gunman who then turned his weapon on himself.
Mr Obama is meeting victims' families and emergency service workers.
He is also expected to speak at an inter-faith vigil at the town's high school.
Ahead of the president's visit, a service for the victims at St Rose of Lima Roman Catholic Church was abandoned and the church evacuated because of an unspecified threat, thought to have been a hoax called in by telephone.
The gunman behind Friday's shootings has been identified by police as Adam Lanza, 20. He shot dead his mother before driving to the school in her car, opening fire on his victims and then killing himself.
Reports say the weapons found at the scene - a semi-automatic rifle and two handguns, as well as a shotgun recovered from the car - were registered to the gunman's mother.
Education officials say they have found no link between the gunman's mother and the school, contrary to earlier reports that said she was a teacher there. Investigators said they believe Adam Lanza attended Sandy Hook many years ago.
Officials say the gunman, armed with hundreds of rounds of ammunition, used the semi-automatic rifle as his main weapon. All the victims were shot several times, some of them at close range.
All 20 children who died in the shootings - eight boys and 12 girls - were aged between six and seven, according to an official list of the dead. The school's head teacher, Dawn Hochsprung, was among the dead.
Connecticut State Police say the process of releasing the victims' bodies to their families is under way, and have condemned what they term "misinformation" being published on social media about the tragedy - including people wrongly claiming to be the gunman.
Gun Control Calls
A nationwide ban on certain semi-automatic rifles in the US expired in 2004.
Shortly after Friday's attack on Sandy Hook school, the president said there must be "meaningful action" against gun crime in the US.
Sunday saw two senior US Democrats call for stricter gun control.
Connecticut Governor Dan Malloy said his state had an existing ban on assault weapons, but the lack of a similar law at federal level made it difficult to keep them out of the state.
"These are assault weapons. You don't hunt deer with these things," he told CNN. "One can only hope that we'll find a way to limit these weapons that really only have one purpose."
Governor Malloy had to break the news to most of the victim's families on Friday.
"You can never be prepared for that - to tell 18 to 20 families that their loved one would not be returning to them that day or in the future," he said.
Senator Dianne Feinstein, who represents California in the upper house of Congress and is a long-term supporter of stricter gun control, told US TV network NBC: "I'm going to introduce in the Senate, and the same bill will be introduced in the House (of Representatives), a bill to ban assault weapons."
Asked if President Obama would support her measure, she said: "I believe he will."
New York Mayor Michael Bloomberg, another strong gun control advocate, has urged President Obama to act.
"We have heard all the rhetoric before," he said. "What we have not seen is leadership - not from the White House and not from Congress. That must end today."
--Courtesy of BBC News