Uvalde shooting: Police admit Texas shooting response was wrong

Police made the "wrong decision" by failing to storm a classroom in Robb Elementary School as a gunman killed 19 children inside, the chief Texas safety official has said.

"If I thought it would help, I would apologise," Steven McCraw said during a heated press conference Friday.

He confirmed a 40 minute gap from the police unit's arrival to when they entered the classroom.

Pupils inside made multiple calls begging for police to come.

The delay in response, now confirmed in a new timeline offered by authorities, has raised even more questions about why 18-year-old Salvador Ramos was inside the school for so long before he was killed - not by local officers, but by a tactical unit led by US border agents.

The gunman crashed his car near the school at about 11:30 local time, Mr McCraw disclosed, and entered the school shortly after - but it was not until 12:51 that a tactical unit breached the door, entering and killing him.

The delay happened in part because the commanding officer on scene believed the situation was no longer one involving an "active shooter", he said.

The description is at odds with the disclosure that at least four emergency 911 calls were made from within the school - apparently from children barricaded inside the classroom where the gunman was firing - asking for police to come.