A powerful cyclone slammed into northeast Australia on Friday, destroying homes, upending trees, cutting power lines and causing flash floods, while a second storm severed communications to a northern island where heavy damage was expected.

Tens of thousands took what shelter they could as Cyclone Marcia caught Queensland state almost unawares, gathering strength in just a few hours before making landfall mid-morning as a category 5 system — the highest rating.

Emergency services scrambled to evacuate thousands of homes before pulling out and warning anyone who had not left to barricade themselves inside to avoid wind gusts peaking at 285 kph (177 mph).

Rail lines to coastal ports, an essential part of Queensland's A$280 billion ($218 billion) commodities export-driven economy, were brought to a standstill.

"Stay indoors, take the safest room in the home and let the storm pass," Queensland Fire and Emergency Services Assistant Commissioner John Watson told media after the storm passed over the coastal city of Rockhampton, home to 75,000 people, and headed south towards Australia's third-largest city, Brisbane.

There were no reports of deaths or injuries and the storm was downgraded to a category 2 by evening. But authorities warned heavy rains and flooding were likely to continue for several days and extend inland.

Some 48,000 homes were left without power, Watson added, broken power lines and flooding leaving some areas too dangerous for energy companies to begin repairs.

The storm roared over the coastal town of Yeppoon which, like Rockhampton, was facing a night without power.

"The home is one of the oldest in Yeppoon," Melanie Cobb told Reuters as she sifted through the rain-soaked contents of her grandmother's 80-year-old house where one wall had been ripped away. Among the ruined contents was Cobb's childhood teddy bear.

More than 10 percent of Australia's sugar crop was at risk from Marcia, an industry body warned. BHP Billiton suspended rail lines hauling coal from its inland collieries to the Hay Point shipping terminal.

Marcia's forecast trajectory indicated the impact on coal mining was expected to be less severe than in 2011, when Queensland missed its annual coal export target by 40 million tonnes after storms dumped unprecedented amounts of rain into pits.

Data supplied by the Bureau of Meteorology showed Marcia moving inland rather than directly impacting the Gladstone industrial hub, where Rio Tinto operates Australia's largest aluminum smelter.

Emergency service officials in the neighboring Northern Territory were beginning to assess the damage caused by Cyclone Lam that made landfall in the remote region east of Darwin.

The category 4 storm hit near the settlement of Ramingining, where residents were beginning to emerge to inspect the damage. Communications had been cut with tiny Elcho Island, which was believed to have experienced widespread damage, police said.

By evening, Lam had been downgraded to a tropical low but continued to dump heavy rain across the north as it moved southwest.