A half-dozen cows that wandered onto a major Ontario highway Saturday morning, blocking traffic for several hours near Hamilton, have been rounded up.

After motorists spotted the cows on Highway 403 around 6 a.m. ET, a stretch of the thoroughfare from Hamilton west to Brantford was closed.

About 30 cows had escaped from a farmer's field and were running loose in the area. Six of them ambled onto the highway.

Ontario Provincial Police Sgt. Dave Woodford said one of those cows charged at police officers and was put down.

All the cows were corralled and the highway reopened not long after 11 a.m., police said.

No injuries were reported.