Hanauma Beach, Oahu, Hawaii. (123rf) A South Korean father and his teenage son were still missing in Hawaii on Thursday, two days after they left their Waikiki hotel for a hike near Hanauma Bay and did not return.The 49-year-old man and his 16-year-old son left the hotel at around 7 a.m. Tuesday to hike the Hanauma Bay Rock Bridge Trail on the eastern side of Oahu, according to the US Coast Guard and local media reports. Their names have not been released.The search has since expanded across land, sea and air, with the Honolulu Fire Department, Honolulu Ocean Safety Department and US Coast Guard joining efforts to locate the pair.Hawaii News Now reported Thursday that there was still no sign of the father and son, who officials believe may have been swept into the ocean off Hanauma Bay.Family members reported the two missing after they failed to return. A backpack containing the father’s belongings, including his phone and wallet, was found near an area known as Rock Bridge shortly before 9 a.m., according to Hawaii News Now.The Honolulu Fire Department found the man’s car near the trailhead entrance, the US Coast Guard said.The Coast Guard said it issued an urgent marine information broadcast and deployed a 45-foot (14-meter) response boat from Coast Guard Station Honolulu and an MH-65 Dolphin helicopter from Air Station Barbers Point after being notified of the missing pair by the Honolulu Fire Department.Search crews have covered more than 30 coastal miles, or about 50 kilometers, from Makapuu Point to Barbers Point, using helicopters, drones, rescue boats, jet skis and divers. Officials have also used data buoys to track currents and drift patterns as they focus on waters off southeast Oahu and Maunalua Bay, according to Hawaii News Now.Weather has complicated the operation. Officials cited choppy waters, a small craft advisory and winds of up to 40 kilometers per hour as factors making the search more difficult.Honolulu Fire Department Capt. Keopele Gowan told Hawaii News Now that the father and son had planned to hike, not swim. Officials said they were experienced swimmers, but search teams were proceeding on the assumption that they may be in the water and need help.Rock Bridge is known locally as a dangerous coastal attraction. Officials said the area has steep cliffs, deep water and a strong surge, and that people have previously been swept into the ocean there.The search was expected to continue through Friday, following what officials described as a standard three-day search protocol.