Police in Massachusetts are warning hikers to be on the lookout for aggressive yaks.

West Springfield police say a hiker in the Bear Hole Reservoir recreation area was charged by three yaks at about 8 p.m. Wednesday.

The West Springfield Environmental Committee posted on Facebook that they appeared docile so someone approached within six feet.

But then "one put its head down, snorted and then charged," and the other two joined in the chase. No one was hurt.

Police Lt. Nolan Ryan says the yaks, native to Asia, all have ear tags and are believed to have escaped from a private owner in nearby Westfield.

Animal control has been notified and has a plan to corral the animals.