Police were told to stop checking people for weapons at the front gates of the Reunion Arena over an hour before the Democratic presidential hopeful appeared on stage on Wednesday, according to a report in Texas newspaper the Star Telegram.

Officers handling security were reportedly ordered to put down metal detectors and to stop checking bags and purses. Several Dallas police officers said they believed it was a lapse in security.

Chief T W Lawrence, head of the Dallas Police's homeland security and special operations divisions, said that while the crowd appeared " friendly" he was still surprised by the great number of people who had entered the building without any checks.

"Doors opened to the public at 10 a.m., and for the first hour security officers scanned each person who came in and checked their belongings. Then, about 11 a.m., an order came down to allow the people in without being checked," the paper reported.

Several other Dallas police officers - speaking on condition of anonymity because the order came from federal officers - told the newspaper it was worrying to see so many people getting in without even a cursory inspection.

"How can you not be concerned in this day and age," said one officer

The Star Telegram said the Secret Service did not return a call seeking comment.

In 1963 John F Kennedy was assassinated in Dallas. The thirty fifth president of the United States was fatally wounded by gunshots while riding with his wife Jacqueline in a presidential motorcade.