Justin Bieber's private jet was so thick with marijuana smoke, the pilots had to wear oxygen masks.

The official incident report said: "The captain of the flight stated that he warned the passengers, including Bieber, on several occasions to stop smoking marijuana."

And the 19-year-old singer and his dad were "extremely abusive" to the flight attendant, prompting her to take refuge in the cockpit.

The report continued: "The captain also stated he needed to request that the passengers stop their harassing behaviour toward the flight attendant and after several warnings asked the flight attendant to stay with him near the cockpit to avoid any further abuse.

"The flight attendant stated the passengers, including Bieber and his father, Jeremy Bieber were extremely abusive verbally and she would not work another flight with them."

When the plane landed, it was met by police and Customs and Border Protection agents, and though the aircraft "reeked" of marijuana smoke, no drugs were found inside the cabin, or in baggage, despite sniffer dogs alerting officers to three of the suitcases on board.

The troubled singer was questioned separately because "in past examinations, Bieber had become argumentative and abusive when together with his security team."

He admitted smoking marijuana and drinking alcohol, but stated that he did not have any additional marijuana.

According to website TMZ, Justin knew the plane would be searched before it even took off because he is on a Homeland Security watch list following his two recent arrests for assault and driving without a valid license, driving under the influence (DUI) and resisting arrest.