A "very destructive" storm has hit the coast of Queensland, Australia, forcing evacuations from coastal communities.
Tropical Cyclone Marcia is bringing strong winds, heavy rain and abnormally high tides.
The cyclone made landfall between St Lawrence and Yeppoon as a Category Five storm but has now been downgraded to a Category Four.
Separately, tropical Cyclone Lam hit the Northern Territory, causing power cuts for thousands.
The storm, which arrived as a Category Four, struck Elcho Island and is moving south-west. Local residents said roofs had been torn off from a number of houses and trees uprooted.
There have been no reports of injuries there, and the storm was later downgraded to Category Two as it continued moving inland.
'Real moving beast'
"The very destructive core of Severe Tropical Cyclone Marcia, with gusts to 250 km/h (155mph), has crossed the Capricorn coast near Shoalwater Bay, and is moving south towards Yeppoon and Rockhampton," Australia's Bureau of Meteorology (BoM) said in a statement.
It said "very destructive winds" would threaten communities between Shoalwater Bay and Rockhampton in the morning, and Capricornia and Burnett districts later in the day.
Local residents should be prepared for an evacuation if advised by the authorities, the BoM added. It also warned about possible tidal and flash flooding.
Queensland Premier Annastacia Palaszczuk said there had been no reports of injuries to people but some reports were coming in of minor structural damage to homes and uprooted trees.
Ms Palaszczuk said 33,000 residences were without power in the Livingstone/Yeppoon area and 20,000 in Rockhampton.
More than 170 schools and child care centres have been closed, and people evacuated or moved to safety on both Lady Elliot Island and Heron Island, on the Great Barrier Reef.
In Yeppoon, about 870 homes were evacuated because of storm surges, according to Queensland emergency authorities.
The mayor of the nearby town of Rockhampton, Margaret Strelow, told ABC Radio that Marcia was like "a real moving beast" as it appeared to head first to the west of the city and then to the east.
Further south, local media reported that 90,000 sandbags had so far been handed out across Queensland's major city, Brisbane, because of predictions of heavy rain and flooding.
Category Five tropical cyclone
Extremely dangerous with widespread destruction
Strongest winds are very destructive with typical gusts over open flat land of more than 280km/h.
These winds correspond to the highest category on the Beaufort scale, Beaufort 12 (Hurricane)
Describing the cyclone as "very serious", Prime Minister Tony Abbott later said: "Let's hope we can get through it... without any loss of life."
A number of people from coastal areas were evacuated before the cyclone hit.
Several towns - including Mackay, Proserpine and Yeppoon, about 670km north of Brisbane - were reportedly in lockdown, establishing emergency centres.
St Brendan's College, a Catholic day and boarding high school in Yeppoon, is being used by emergency services as one of the evacuation centres for local residents.
Principal Nick Scully told the BBC that about 220 students had left the school on Thursday to travel home to their families but another 40 boys, mostly from the Torres Strait Islands in northern Australia, remained at the school.
About 350 local residents are sheltering in the school's chapel.
"The winds are starting to pick up, there are some thumping noises and the trees are being pushed down," said Mr Scully.
"But it has not hit that freight train like noise [some cyclones get] so I think we are a little way away from the worst," he said.
In 2013, powerful tropical cyclone Oswald hit Queensland, killing at least four people and flooding wide areas.