SYDNEY (AFP) - A monster cyclone roaring towards a heavily-populated area of Australia will be a "calamity", officials said Friday while warning residents to prepare for "a harrowing and terrifying experience".

Tropical Cyclone Marcia is expected to slam into the Queensland coast Friday morning and cause significant damage after being upgraded to a category five, the most severe.

Current forecasts have the tempest, which is around 70km in width, making landfall near the town of Yeppoon, some 670km north of Brisbane.

Massive seas, a deluge of rain, flash flooding and wind gusts of up to 295kmh are expected along with abnormally high tides.

"This is going to be a calamity, no doubt about that," Queensland Police Commissioner Ian Stewart said, adding that it was a "desperate situation".

"Our primary focus from this point on is the safety of all human life in that area."

The cyclone is expected to cause significant damage, the Australian Bureau of Meteorology's senior forecaster Sam Campbell said.

"This is an extremely dangerous system," he told national broadcaster ABC.

"There's likely to be significant damage to roofs, buildings, debris flying through the air, widespread power failures and really the potential for widespread destruction over the warning area."

Queensland Premier Annastacia Palaszczuk said the full brunt of the storm would be felt around the Yeppoon area.

Once it crosses the Capricorn coast it will continue south before easing to a category three, she said.

"Over the next few hours, many thousands of Queenslanders are about to go through a harrowing and terrifying experience and I want those people to know that we are with you every step of the way," she said.

"We will be standing by your side. This a severe cyclone. I want everyone to take all the precautions that they possibly can take."

She added that people around Yeppoon and low-lying coastal areas were being evacuated.

The area is home to around 16,000 people.

In a rare occurence, a second big storm - Tropical Cyclone Lam - crossed the coast further north just hours earlier after intensifying to a category four overnight.

That area, around the Northern Territory Aboriginal communities of Milingimbi and Gapuwiyak, is far less populated.

Meteorologists described both storms as having a "very destructive" core.