BBC News - PSNI helicopter crashes in the Mourne mountains
Emergency services are on their way to Hilltown, County Down after receiving a report that a police helicopter has crashed.
It is believed four people are on board.
The helicopter was on lease to the PSNI.
It is understood the accident happened close to where a private helicopter crashed at the weekend killing three people.
On Saturday, three people were killed in a helicopter crash in the Mourne Mountains in an area known locally as Leitrim Lodge, between Hilltown and Rostrevor.
Charles Stisted, Ian Wooldridge and their pilot, who has not yet been named, died when the aircraft crashed.
The men were travelling back to England from County Tyrone, where they were part of a private shooting party at Baronscourt country estate.
Mr Stisted, 47, was chief executive of the Guards Polo Club at Windsor and a personal friend of the Prince of Wales.
Mr Wooldridge, from Windlesham, Surrey, was also a member of the Guards Polo Club.
Together with his brother Graham, he ran a £40m-a-year demolition and construction company.
Mr Wooldridge was a prominent figure in Dublin-based Harcourt Developments, the property company involved in the development of the Titanic Quarter in Belfast.