So serious is the situation in NSW that Premier Dominic Perrottet issued an urgent warning of the need for people to evacuate as the situation is expected to worsen later this week.

Hundreds of people in the north of the state have been left stranded for hours on rooftops as state and federal emergency services struggle to access impacted areas. Four Australian Defence Force aircraft are waiting to join the rescue effort while RFS strike teams also are involved in what has been described as a "natural disaster of unprecedented proportions".

Just before 3pm, the Bureau of Meteorology said the Wilsons River at Lismore was at 14.37m but may rise further. The previous peak was 12.27m in 1954.

The news is no brighter in Queensland where a Gold Coast man and his dog have been swept to their deaths as Queensland's flooding crisis moves south.

The man, aged in his 50s, and his dog died when their car was swept away in torrential rain about 3am Monday. His death is the eighth fatality in south-east Queensland's floods as rising water levels inundate thousands of homes and businesses.

Earlier this afternoon Brisbane's Story Bridge was closed after a pontoon carrying a crane broke free from its mooring.

And other states are dealing with wild weather, too. Residents of eastern Tasmania are being warned to brace for severe thunderstorms and potentially dangerous flash flooding in some areas.

The situation in Ukraine is no less tense, particularly since Russian President Vladimir Putin ordered his military command to put nuclear-armed forces on high alert.

The announcement does not mean Russia intends to use the weapons but condemnation was immediate all the same. The US called it an "unacceptable escalation".

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