After a day of “rigorous aerial searching,” there has been no confirmed sighting of the U.S. Marine helicopter from Camp Pendleton reported missing in Nepal, officials said Wednesday.

The UH-1Y Huey was on a disaster relief mission when it disappeared Tuesday. Onboard were six Marines and two members of the Nepalese military.

The search included other Marine aircraft and U.S. Air Force rescue specialists. The effort will resume when daylight returns Thursday.

“We remain optimistic in our efforts,” said Army Major Dave Eastburn, spokesman for the U.S. Pacific Command. He said the U.S. mission in Nepal “has multiple aircrews available to ensure they can maximize the time in the air searching for the missing Huey.”

A battalion-sized Nepalese ground force has moved into the area to search, officials said.

The Huey was in the Philippines on a training mission when it was ordered to join the earthquake relief effort in Nepal. After taking on supplies at Clark Air Base, the aircraft and others from the same squadron flew to Kathmandu.

The chopper is assigned to Marine Light Attack Helicopter Squadron 469 at Camp Pendleton in California. It did not send any distress message before it disappeared while taking supplies to villagers in the rugged area of Charikot, officials said.