In the aftermath of the Connecticut mass school shootings, some politicians, including President Barack Obama, have called for action to prevent similar episodes in the future.
Outside the White House, demonstrators demanded immediate action after 20 children and six adults, including the killer's mother, were shot dead at Sandy Hook School in Newtown in the north-east of the state.
The gunman is also dead and another body believed to be that of his father has been found at a nearby house.
Mr Obama spoke emotionally of the 20 children saying the hearts of Americans were broken by the tragedy. He said the country had been through the same thing too many times and needed to take meaningful action.
One Democrat congressman said if now wasn't the time for a serious discussion on gun control he didn't know when it would be.
The mayor of New York Michael Bloomberg condemned what he called a lack of leadership on the issue from both the White House and the congress.
But the BBC reports that despite a number of high profile mass shootings over the past two years, there seems little appetite for stricter gun control.
It reports that most Americans still believe gun ownership is guaranteed by the consitution and support for stricter legislation has fallen dramatically in recent years.
But there has also been a gradual decline in the overall level of gun crime.
"There must have been 100 rounds"
Eighteen children were pronounced dead on Friday at the school and two more children died in hospital.
Connecticut State Police said six adults were dead.
Lieutenant Paul Vance said the shootings took place in two rooms within a single section of the school.
The gunman's body was found inside the main building. He killed his father before going to the school to kill his mother who worked as a teacher there.
WABC reported he was armed with four weapons and wearing a bullet-proof vest.
Early reports named Ryan Lanza, 24, as the gunman, but officials later said his brother Adam, 20, was the suspect. Adam Lanza once attended Sandy Hook School.
The New York Times reported Ryan Lanza was being questioned by police.
Three people are in hospital. Danbury Mayor Mark Boughton told CNN they are in "very serious condition".
Police also said there was another victim at a second crime scene, but did not provide details.
The incident began while the pupils were in their classrooms at the start of the school day. Police arrived at the school soon after 9.40am on Friday.
The BBC reports children were evacuated from the school and others across the district are on lock-down as a preventive measure.
As the situation began, police received a call reporting that a gunman was in the school's main office, the Hartford Courant newspaper said.
One witness told CNN said that shots were heard coming from the hall. There "must have been 100 rounds" fired, she said.
The BBC reports Sandy Hook School has more than 600 students ranging from kindergarten to 4th grade.
A statement on its website said its kindergarten class is cancelled on Friday and midday bus runs will not operate.
This is the second-deadliest shooting in US history, after an attack at Virginia Tech university killed 32 in April 2007.
Friday's shooting is also the third major shooting in the United States this year.
In July, 12 people were killed at a premiere of a Batman film in Aurora, Colorado. In August, six people died at a Sikh temple in Wisconsin.
Our hearts are broken: President Obama
From the White House a clearly emotional President Barack Obama spoke about the tragedy.
"They had their entire lives ahead of them, birthdays, graduations, weddings, kids of their own," said President Barack Obama in Washington DC.
''Our hearts are broken today, for the parents and grandparents, sisters and brothers of these little children and for the families of those who are lost.
Speaking as a parent, Mr Obama offered condolences to the families of those who survived, saying "their children's innocence has been torn away from them too early and there are no words that will ease their pain".
"As a country we have been through this too many times," Mr Obama said, mentioning earlier shooting massacres, in Colorado, Oregon and Wisconsin.
"These neighbourhoods are our neighbourhoods, these children are our children.
"We are going to have to come together and take meaningful action to prevent more tragedies like this regardless of the politics."
World leaders express shock and sympathy
United Nations chief Ban Ki-moon has written to Connecticut Governor Dan Malloy to give his deepest condolences.
The Queen and the leaders of the European Commission, France, Britain and Canada have all sent messages expressing their shock and sadness.
Australian Prime Minister Julia Gillard said Australia shared America's shock at the senseless and incomprehensible act of evil.
John Key has described the massacre as random, needless and heartbreaking and was sending his heartfelt condolences to the families of the victims, the staff and teachers of the school, and the whole community.
United States Ambassador to New Zealand and Samoa, David Huebner says he's shocked and overwhelmed.
In a written statement, Mr Huebner says his thoughts and prayers are with the victims and their families and others affected by "this horrendous tragedy".
He thanked New Zealanders for their expressions of sympathy and condolence to America on the tragedy.