N. Ireland's richest man killed

An entrepreneur and politician who was Northern Ireland's richest man has been named among four people killed in a helicopter crash in thick fog in eastern England.

Lord Ballyedmond, a Conservative peer in the House of Lords, was in the twin-engined AgustaWestland AW139 when it came down near the town of Beccles in Norfolk on Thursday.

The 70-year-old, known as Edward Haughey until made a peer in 2004, was founder and chairman of Norbrook, a veterinary pharmaceuticals company.

Haughey owned Gillingham Hall, a stately home near the crash site. His personal fortune was worth STG860 million ($A1.59 billion), according to The Sunday Times newspaper's Rich List 2013.

Reports said Ballyedmond's company Haughey Air Ltd lodged a writ against AgustaWestland last year over concerns about the in-flight mapping systems of a helicopter supplied by them.

A spokesman for AgustaWestland said it could not comment on possible defects with Lord Ballyedmond's helicopter but said it was investigating.

Officers were called to the accident scene after members of the public reported a loud crash, Norfolk police said.

"The crash site is in a field containing some wooded area and all four occupants on board the helicopter were pronounced dead at the scene," the force said in a statement.

Only a limited investigation of the site had been possible in the dark and foggy conditions and a more detailed forensic examination was due Friday, they added.

Early reports suggested the helicopter was heading to Northern Ireland, though police refused to comment on its departure point or its planned destination.