Police have received reports of a sheep and lambs being chased and attacked by a large dog in a field near St Johns Lane, Cranford.
The incident happened between 7:30am and 8am yesterday (Sunday, 24 April).
Three lambs subsequently died, five are being treated and others sustained minor injuries.
Officers are reminding dog owners that it is an offence to have a dog off a lead or not under close control in a field of sheep, or to let their dog chase or attack livestock.
Officers would like to speak to anyone who may have witnessed this incident or who may have any information regarding it.
Witnesses or anyone with information about this incident can contact police on 101 or Crimestoppers anonymously on 0800 555 111.