The US Coast Guard says a tour helicopter with seven people on board is missing off the coast of Hawaii.
The aircraft was carrying a pilot and six passengers, with the passengers reported to include two children.
Emergency services were alerted at around 6pm on Thursday local time, after the aircraft failed to return as planned 45 minutes earlier.
Officials say the helicopter - which was on a tour of Kauai's Nā Pali Coast - was fitted with an electronic locator, but no signals have been received.
Rescue teams say the weather conditions in the area "are challenging".
Robert Cox from the Coast Guard Joint Rescue Coordination Centre Honolulu said: "We have trained crews responding and on scene searching for any signs of the helicopter and those aboard."
Authorities added that a fresh helicopter crew was prepared to join the search at first light if needed.
