SYDNEY, AUSTRALIA -- Australia on Sunday warned of a "high risk" of terror attacks on domestic and international flights in and to the United States, urging citizens to be vigilant while in the country.

"We advise you to exercise caution and monitor developments that might affect your safety in the United States because of the risk of terrorism," the Department of Foreign Affairs and Trade said in a travel advisory.

The department urged travelers to monitor the media for information about possible new security threats.

"The United States Department of Homeland Security's Advisory System Threat Level is at Orange for all domestic and international flights, indicating a 'high' risk of terrorist attack," it said.

"It is at Yellow or 'elevated' for all other sectors, indicating a significant risk of terrorist attack."

The advisory also included warnings about extreme weather conditions as Hurricane Gustav bears down.

"There is severe weather, including hurricane conditions, affecting the southeast coastline of the United States," the advisory said.

"Australians in affected regions should adhere to all advice and evacuation requests enforced by local authorities."

New Orleans began mandatory evacuations as Gustav, hailed as "the mother of all storms", was set to plow into the US Gulf Coast on Monday packing winds of 150 miles (242 kilometers) per hour.