LONDON (AP) — Hundreds of motorists were stuck for hours on one of Britain's main highways after it was closed Tuesday due to a "suspicious object."

The M1 motorway was shut along a 10-mile (16-kilometer) stretch near Milton Keynes, 50 miles (80 kilometers) north of London, after the object was found under a bridge at around 7:30 a.m., Thames Valley Police said.

Photographs on social media showed people playing Frisbee and kicking a soccer ball on the empty road.

"There's a five-a-side football competition, a bit of rugby, a guy cycling up and down in the wrong direction," said Tim Mayer, who was caught up in the delay.

Seven hours after the object was found, police said the bomb-disposal squad had determined it contained "no explosive element" and appeared to be "some form of chemical."

Chief Inspector Mark Lewis said the object contained "a highly corrosive substance" that had leaked across the road.

"There is no evidence to suggest that this is a terrorist incident," he said.

By late afternoon, police said the northbound highway had reopened and vehicles that had been trapped in the southbound lanes were being allowed to leave by a detour.