Sydneysiders were forced to kick off their doonas last night as the city sweated through its seventh sleep above 24 degrees Celsius — a new summer record.

Sydney's Observatory Hill, at The Rocks, has recorded nine days of temperatures 35C and above, equalling the previous record set more than 120 years ago in the summer of 1895–96.

The area also recorded its warmest January ever for average maximum, minimum and mean temperatures.

"We've had very warm temperatures in Sydney for both days and nights," Bureau of Meteorology senior climatologist Agata Imielska said.

"The fact that we've had none of these particularly cool days coming through, no very strong cool southerly changes, I've found that particularly unusual and just hard to deal with without an air conditioner at home personally.

"It's just been back-to-back really warm conditions."

Last night, the lowest temperature was 25.4C in Sydney, while the average minimum for the city in the month of January is 18.7C.

"We're looking at almost 10 degrees [Celsius] above the average," Ms Imielska said.

A lion at Hunter Valley Zoo tucks into a blood ice block today in an attempt to cool down. ( Supplied: Hunter Valley Zoo )

More records for Moree

Moree, in the state's north, has sweltered through 36 straight days of at least 35C weather.

Moree cotton farmer Sean Young can still crack a smile despite the record temperatures. ( ABC News )

The current stretch is more than twice as long as the previous record, set in 1981.

Cotton farmer Sean Young said the weather was taking its toll.

"This heatwave's absolutely roasting the cotton and it's chewing up our natural resources, mainly water," he said.

"We've got cotton now and it's at that stage now where it really needs a drink."

Fellow cotton farmer Dick Estens shared similar sentiments.

"We've lacked summer storms, you know, cotton love storms," he said.

"We live on hope in the farming game, if the people of Bondi can give us a little rain dance that would be good."

But a cool reprieve is unlikely, with Moree forecast for another week where temperatures sit each day at between 40C and 44C.

Mayor Katrina Humphries said enduring the tough weather was part of rural life.

The whinging city cooler than the west

Western Sydneysiders may scoff at the whinging of those in the city's east, having set records for the number of days with above 40C weather this month.

Those in Richmond have battled seven days above 40C so far, with that figure expected to rise this week with three more days and a top of 44C forecast for Sunday.

Penrith also experienced 23 days of above 35C weather and eight days that hit above 40C.

Ms Imielska said dry and warm conditions will continue for the next three months across the entire state.

"[We're] not seeing much of a relief in terms of the persistence of those dryer and warmer conditions," she said.

"Eventually the heat will break but it'll really be a matter of when."