A tour helicopter carrying seven people — two of them reportedly children — went missing off the coast of Hawaii, officials said.

The aircraft, which had embarked on a tour of Kauai’s Nā Pali Coast, was due back at 5:21 p.m. Thursday, the Coast Guard said in a statement. One pilot and six passengers were on board.

When it didn’t return by 6:06 p.m., the owner of the helicopter raised the alarm with Coast Guard watchstanders.

The aircraft is equipped with an electronic locator, but no signals were received, according to authorities.

The Coast Guard launched a thorough search — deploying helicopters and one of its cutter vessels. Further searches are scheduled at first light.

“The weather conditions are challenging,” Petty Officer 1st Class Robert Cox, of the Coast Guard’s Joint Rescue Coordination Center in Honolulu, said in the statement. “We have trained crews responding and on scene searching for any signs of the helicopter and those aboard.”

During the initial search, rain and clouds were limiting visibility to around 4 miles and winds were around 28 mph, the Coast Guard said.

Friday’s weather is expected to bring 23 mph winds, waves at 6 feet and scattered rain showers.