The crowd waiting to buy 1,000 used laptop computers for $50 each turned into a mob in Richmond Tuesday morning.

Henrico County authorities said that about 5,500 people showed up for the sale at the Richmond International Raceway. And after waiting for hours, when the gates opened at 7 a.m., it became a mob scene.

Police said a girl’s stroller was crushed in the stampede. Blandine Alexander, who brought her 14-year-old twin boys to the complex at 4:30 a.m. to wait in line, called the mob scene terrifying.

She said an elderly man was thrown to the pavement and someone in a car tried to drive his way through the crowd. Alexander said a woman standing in front of her wet herself to keep from losing her place in line to go to the bathroom.

Battalion Chief Steve Wood said 17 people suffered minor injuries in the rush, with four requiring hospital treatment. There were no arrests.

The 4-year-old Apple iBooks, retail for between $999 and $1,299. The Henrico County school system was selling 1,000 of the computers to county residents.