Mourners in the US town of Newtown, Connecticut gathered this afternoon for the first two of 20 funerals of children shot dead in their classroom.

The town's schools remained closed after a weekend of mourning that followed Adam Lanza's attack at Sandy Hook Elementary School on Friday.

The 20-year-old killed 27 people in the attack, including his mother at her home, before taking his own life.

Miniature caskets marked the first wave of funerals as Noah Pozner and Jack Pinto, both six years old, were laid to rest this afternoon.

Jack was buried in his hero's New York Giants football jersey in a small white coffin.

Balloons and a teddy bear welcomed mourners to the funeral of his first grade schoolmate Noah, who was the youngest victim. His twin sister, Arielle, escaped unhurt.

The shooting has caused anxiety across the country.

Within hours of the school starting bell this morning, lockdowns were declared in nearby Connecticut and New York towns.

In southern California, Indiana and Tennessee, authorities arrested men yesterday for making threats against schools.

Police and bomb-sniffing dogs conducted a precautionary search of the street lined with white balloons outside the Fairfield, Connecticut, funeral home where Noah's life was remembered.

A teddy bear and bouquet of white flowers lay at the base of an oak tree outside the Jewish service that was packed with mourners, including Connecticut Governor Dannel Malloy, US Senator Richard Blumenthal and Senator-elect Chris Murphy.

"Noah was an impish, larger-than-life little boy," his family said in his obituary in the Newtown Bee newspaper.

"Everything he did conveyed action and energy through love. He was the light of our family, a little soul devoid of spite and meanness," wrote his parents, Lenny and Veronique Pozner, and four siblings.

At Jack's funeral in Newtown, about a half dozen children wearing a wrestling's club gold medals took off the awards and gave them to their teammate's parents.

A New York Giants fan, Jack was wearing a red-and-white jersey with receiver Victor Cruz's number 80 as he lay in an open white casket at the service.

During an NFL match yesterday, Cruz wore shoes with "RIP Jack Pinto" written on the side.

"Jack was an incredibly loving and vivacious young boy, appreciated by all who knew him for his lively and giving spirit and steely determination," his parents, Dean and Tricia Pinto, and brother said in his obituary in the Newtown Bee.

Active in sports from football to skiing, he was remembered "for the immeasurable joy he brought to all who had the pleasure of knowing him, a joy whose wide reach belied his six short years".

Their funerals came a day after President Barack Obama visited Newtown to comfort the families, promising action to stop future tragedies.

Mr Obama's remarks were heralded this morning by relatives of teacher Victoria Soto, 27, who was killed as she tried to protect her first-grade students.

"He really made us feel like she really was a hero and that everyone should know it," her younger brother, Carlos Soto, told CBS "This Morning".

A White House spokesman said tonight that Mr Obama's plan for action to curb violence includes gun control "but is far from all of it".

All the dead children were six or seven years old. The school principal of Sandy Hook Elementary, the school psychologist and four teachers were also murdered.

Further details of massacre emerge

A more detailed picture of Lanza's stunning attack has emerged.

After killing his mother, Nancy Lanza, at home, Lanza shot his way into the school.

He had attended Sandy Hook as a child, according to former classmates, but authorities said today he had no current connection with the school.

Police said Lanza was armed with hundreds of bullets in high-capacity magazines of about 30 rounds each for the Bushmaster AR 15 rifle and two handguns he carried into the school.

A fourth weapon, a shotgun, was in his car outside. He killed himself in the school.

In Washington, a growing number of US politicians, including a leading pro-gun senator, called for a look at curbing assault weapons, such as the one used in the massacre, a sign that attitudes toward gun control could be shifting.

"Never before have we seen our babies slaughtered. This never happened in America, that I can recall, ever seeing this kind of carnage," said Senator Joe Manchin, a West Virginia Democrat.

"This has changed where we go from here."