Signalling the onset of La Nina, heavy rains battered the northern coast of Australia over the weekend that mostly dampened Christmas celebrations in the region while allowing some rays of sun in the far east of the country.

While Australia's northern parts were pummelled by gusty winds and storm surges due to Tropical Cyclone Grant, forcing many residents to a subdued celebration of the long holiday breaks, beach goers in Sydney took advantage of the good weather after enduring weeks of almost continuous rains.

The country's weather bureau, according to Agence France Presse (AFP), has reported that Grant would gradually gather more strength, packing winds of up to 130 kilometres per hour, making the cyclone extremely deadly for Aussies wishing to venture out.

Officials have issued advisories urging Darwin residents and neighbouring areas to stay indoors and hunker down until the full effect of the storm settles, the AFP said.

Grant, weather authorities said, would further intensify as it moves inland.

They added, however, that the cyclone would weaken a bit once it makes landfall early Monday but would eventually regain its old strength once it reaches the Van Diemen Gulf.

While far away from Grant's path, Melbourne officials have reported of a tornado that had hit northwest of the city, according to the State Emergency Service (SES) news release, hitting the metropolis in the immediate aftermath of Cyclone Fina's paralysing impacts.

"There was a tornado reported at Fiskville and we know it touched down at Keilor Downs because we had some SES volunteers there and they had to run for shelter," SES spokesman Lachlan Quick was reported by AFP as saying.

Yet up north from Melbourne, Sydney residents bathed under the rare sunlight as officials reported that thousands hit the city beaches to briefly get a taste of the waters following weeks that mostly soak, chilly and gloomy despite the holidays.

Weather officials warned that more storms and cyclones would follow after Fina and Grant and the rainy conditions would likely extend over the next few months as cool winds from the Pacific Ocean are projected to spawn more weather disturbances, with authorities attributing them to La Nina.

The same weather systems whipped Northern Australia earlier this year, shutting down mining sites and leaving behind widespread destructions that undercut growth of the national economy in the first half.