US President Joe Biden has visited an elementary school in Uvalde, Texas, to meet and console the families of victims and survivors of last week's deadly mass shooting.

The president, along with First Lady Jill Biden, visited the Robb Elementary School on Sunday.

They laid flowers at makeshift shrines and offered prayers for the 19 students and two teachers who were killed by an 18-year-old gunman who stormed the school on Tuesday. Biden met their bereaved families afterward.

People who gathered on the streets chanted, "Do something," and Biden replied, "We will."

It has been revealed that police officers who rushed to the scene did not immediately breach the classroom where the gunman had barricaded himself. They instead waited in a hallway for about 45 minutes. The gunman was eventually shot and killed by border patrol agents.

The US Justice Department says it will conduct a review of the law enforcement response to the mass shooting.