Police in Massachusetts are treating the case of missing Brockton girl Brittany Bransfield as a runaway, not an abduction.

Brittany, 16, was last seen Saturday afternoon after telling her mother she was going across the street, the Brockton Enterprise reported.

"It's not like her. She's not answering her phone, nothing," Chris Bransfield, Brittany's father, told the paper, adding that his daughter never ran away from home before.

Meanwhile, police said Tuesday morning that a 15-year-old girl who authorities believe was with Brittany when she went missing is now in custody. It’s unclear whether the second girl was believed to be involved in Brittany’s disappearance.

"This appears to be a runaway situation, and not an abduction," Brockton Police Lt. Paul Bonanca said.

Brittany, a student at Brockton High School, was described as 5-feet-7, 110 pounds with long brown hair. Anyone with information on the missing girl was urged to call the Brockton Police Department at 508-941-0200.