The tragedy at Sandy Hook Elementary School, Newtown, Connecticut, has cast a pall of gloom over the entire United States.

The incident has shocked countless children and parents who are not even remotely connected with the heart-wrenching incident.

It is still worse for the 600-odd children who attend the school. Rescue teams told children to close their eyes while leaving the school, but it is feared that the shooting could scar their young minds for life.

"Everybody was crying. And I just heard the police officers yelling," eight-year-old Alexis from the school told CNN while being hugged by her mother, Lynn. "My heart is in a million pieces for those families," said Lynn Wasik. "Who could do something like this? It's just sickening."

According to eye witnesses, as many as "100 gunshots" were heard. No motive for the killings has yet emerged.

While one of the teachers locked students in a classroom cupboard, another told children to take cover in a corner of the room, saving many lives. The gunman had attacked two adjoining classrooms.

Nine-year-old Geneva Cunningham was in the library when the gunman struck. She heard "a lot of screaming and yelling". Geneva told the Los Angeles Times: "They [teachers] told us it was a drill and that it was for our own safety. When it was happening there was a lot of glass shattering."

Hundreds of people held candlelit vigils across the country, including outside the White House. Connecticut Governor Dannel Malloy said the shooting was a "tragedy of unspeakable terms" adding that one "can never be prepared" for such an attack.

"Evil visited this community today and it's too early to speak of recovery, but each parent, each sibling, each member of the family has to understand that Connecticut - we're all in this together. We'll do whatever we can to overcome this event," added Malloy.

While David Cameron was "shocked and deeply saddened" by the incident, Australian Prime Minister Julia Gillard dubbed the gunman's actions a "senseless and incomprehensible act of evil".

This is the third major gun attack in 2012 after the Colorado rampage at a movie premiere in July and the Sikh temple massacre in August.

"There is going to be a black cloud over this area forever. It will never go away," Craig Ansman, the father of a four-year-old girl at the school told the New York Times.

A woman prays at Saint Rose of Lima Roman Catholic Church near Sandy Hook Elementary School, where a gunman opened fire on school children and staffReuters
Candles burn in Oakland, California, to commemorate the victims of the Connecticut elementary school shootingReuters
Aminah Crawford joins a vigil in Oakland, California, to commemorate the victims of the Connecticut elementary school shootingReuters
Andrew Jacobs, left, prays as his twin brother Matthew looks on outside Saint Rose of Lima Roman Catholic Church near Sandy Hook Elementary School, where a gunman murdered school children and staffReuters
People attend a vigil service at the St. Rose of Lima Roman Catholic Church for victims of the Sandy Hook Elementary School shooting in NewtownReuters
A woman comforts a young girl during a vigil for victims of the Sandy Hook Elementary School shooting in NewtownReuters
Farah Sheikh takes part in a candlelit vigil in Times Square, New York, for the victims of the Sandy Hook School shootingReuters
People flee from the scene of a ghastly shooting incident at the Sandy Hook Elementary School in Newtown, Connecticut, December 2012.Reuters
Parents arrive at the scene of the shooting incident at Sandy Hook Elementary School in Newtown, ConnecticutReuters
People leave the scene of the shooting incident at Sandy Hook Elementary School in Newtown, ConnecticutReuters
A US flag flies at half mast in front of the Reed Intermediate School in Newtown, Connecticut, following the shooting at nearby Sandy Hook Elementary SchoolReuters
The families of victims grieve near Sandy Hook Elementary School in Newtown, Connecticut, where a gunman opened fire on schoolchildren and staffReuters
Residents peer through a police cordon around the Sandy Hook Elementary SchoolReuters
U.S. President Barack Obama wipes away a tear as he speaks about the shooting at Sandy Hook Elementary School in Newtown during a press briefing at the White House in WashingtonReuters