F18s reportedly scrambled for G20 security scare TWO F18s were scrambled in a G20 security scare yesterday. Fighter jets rushed to investigate an unknown radar track about 7.40am off Bribie Island to discover it was just a boat. Defence later released a statement to media that the two hornets had been launched from RAAF Amberley to investigate an unknown radar track. "Upon investigation the object was identified as a ship at sea," the statement said. The two aircraft then continued on their normal air patrol tasking support to the G20 Leaders Summit. One was believed to be a Cape Byron Patrol vessel operated by Australian Customs. The second was listed as the Hugli Spirit, a large chemical ship from the Bahamas. Meanwhile, police have confirmed two civilian planes were intercepted in restricted Brisbane airspace last night. "Police spoke to the pilot of a plane that was intercepted late yesterday afternoon, south of Brisbane," the spokesperson said. The man made contact with authorities after the incident, when he realised he had entered the restricted airspace. "At no time did either aircraft pose a threat to the security of the G20 Leaders" Summit." Civil Aviation Safety Authority will be investigating both incidents. Crestmead resident Kai Draper said he witnessed a light aircraft being tailed by two Super Hornets flying low over his house south of Brisbane about 6.30pm. The planes circled the area for about ten minutes followed by a police helicopter. He said light aircraft often flew in and out of a nearby a private airstrip at Logan Reserve but he had never seen military aircraft in the area. "I heard a lot of racket so I looked out the window and saw a Super Hornet flying across," Mr Draper said. They were pretty low and over the top of our house. Then I saw a little Cessna, or a little light aircraft, travelling from west to east towards a little private airstrip here. They hung around for about five minutes and then flew away again, and then PolAir came for a visit about 10 minutes later. They just flew around in the air above him and crossed his path in front of him. Sunday's security scares followed police investigating "mysterious" bubbles in the Brisbane River on Saturday. When bubbles were spotted in the river five police boats rushed to the scene to ensure the safety of our international leaders. But as social media lit up with theories of what could have caused the bubbles - including Putin in a submarine - police pulled back. According to police, the bubbles came from a grate on an outlet pipe. The incidents came as security forces were on high alert, with the world's leaders gathered in Brisbane for this weekend's summit. Around 6000 police officers patrolled the streets, with military personnel and SES volunteers providing further back-up. Roads and hotels were barricaded, and even catering trucks could not move through the city without police escorts. Helicopters whirred overhead, and each of the G20 nations had also brought its own private security detail. Major disruption and delays are being experienced this evening with 20 of the 26 leaders leaving the city in motorcades at the close of the conference. Several protests went ahead today, following more than 20 yesterday.. There were just four arrests during yesterday's protests, with 24 people excluded from the security zone around the CBD. Officials had warned things could get "brutal" in the city, with temperatures expected to soar to 40C, but another relatively peaceful day proceeded. Security did, however pounce on a man with two suitcases near the Marriott Hotel, where US President Barack Obama was staying. He was detained and searched this morning just metres from the hotel.