Four people who survived when a sightseeing helicopter crashed at the Grand Canyon earlier this month are still in hospital in critical condition.

Three British tourists were killed on February 10 when the helicopter from Las Vegas went down on tribal land outside Grand Canyon National Park.

The pilot and three other Britons were injured and taken to a Las Vegas trauma centre.

A spokesman for University Medical Centre of Southern Nevada says the four survivors are still listed in critical condition as of Sunday.

The cause of the crash is being investigated by the US National Transportation Safety Board.

Preliminary findings are expected before the end of the month, though a full report on the crash will not be done for more than a year.

Becky Dobson, 27, Stuart Hill, 30, and his brother Jason Hill, 32, were killed in the incident.

Britons Ellie Milward, 29, Jonathan Udall, 32, and Jennifer Barham, 39, were injured in the crash, along with pilot Scott Booth, 42.