Story highlights

NEW: Loved ones report three Marines missing; CNN affiliate reports a fourth

Crews search wreckage seven miles offshore between Mokule'ia Beach and Turtle Bay

"It is very difficult to find things right now," Coast Guard says of weather during search

CNN  — 

Crews are searching for 12 Marines missing at sea after two CH-53 helicopters apparently collided during an overnight training flight off the Hawaiian island of Oahu, authorities said.

Personnel from the U.S. Coast Guard, Navy, and Honolulu Fire Department looked for survivors seven miles offshore in increasingly poor weather conditions. Swells reached 16 feet, surf rose to 40 feet and visibility extended to only one mile, the Coast Guard said.

“The weather is making it very difficult,” Coast Guard spokesman Lt. Scott Carr told reporters. “It is very difficult to find things right now.

“Our goal is to find survivors,” he said.

Loved ones of missing

Orlando’s family asked for prayers for him and the other missing Marines. “We would like to thank everyone who continues to pray and send their expressions of concern and love for the safe return of United States Marine Corps Cpl. Christopher Orlando and his fellow Marines,” they said.