Rats are on the rampage in Sydney's inner suburbs with the proliferation of new cafes and booming rental market creating perfect conditions for the rodents to flourish.
Older suburbs close to the city where landlords fail to carry out maintenance and residents dump their rubbish in plastic bags are creating havens for Sydney's two major rat species.
Businesses and residents are reporting sightings of rats, including brazen appearances in full view on streets and in backyards.
Some residents complained of rats almost the size of cats, but rat experts say the brown or sewer rat grow to a maximum of 25cm with a tail of similar length, while black or roof rats are smaller.
Stuart Jackson, who has been treating rat infestations in Sydney for 40 years, told news.com.au that an increase in demand for rat control has seen him called out to outbreaks at commercial and residential properties.
"It has always been consistent but there is an upsurge in calls particularly in the older suburbs like Surry Hills, Haymarket and in the city itself," Jackson, of Expert Pest Control, said.
"There's the old dunny lanes, neglected properties with inadequate waste control, poor hygiene standards and places where they dump their rubbish in plastic bags in the backyard.
"Plastic bags are no deterrent to a rat and the waste goes down a drain where [the brown rat] Rattus Norvegicus live.
"I was called to an advertising agency where they have meetings in the boardroom and watch the rats running up the wall from the property next door.
"A lot of it could be easily prevented, but you have $2m to $3m properties in the inner city next to a rental where the landlord doesn't care and where there's broken pipes or tiles and the rats burrow underneath.
"And there are restaurants which just don't dispose of their waste properly. I won't name them."
Jackson described a "horror" scene he once witnessed in an inner city restaurant where he was called in and found 50 rats clustered around the hot water service under the stairs close to the restaurant's garbage compactor room.
He has also seen rats running through serving kitchens and under sinks in high density restaurant areas like Haymarket, in Sydney's CBD.
Ecologist and rodent plague expert Professor Mathew Crowther of Sydney University said that while current rat numbers in Sydney "could not be called a rat plague, there are more rats than people in Sydney and we have created the perfect habitat for them".
Brown rats live in drains, sewers, under pavers and in dry areas under piles of wood or furniture discarded in yards.
Black rats, Rattus Rattus, are the rodents that can be heard scurrying around in roofs at night when they venture out to feed on garbage, snails and other bugs on shrubs, citrus fruit and even macadamia nuts.
"They are very agile and live in wall or roof cavities. They forage at night and you can hear them when you are lying in bed," Jackson said.
"Rattus Norvegicus will burrow and excavate under foundations and broken concrete and then come out at night as scavengers. Occasionally you will see one running along your back fence.
"You can do everything possible yourself like repairing holes and removing rubbish, but if your neighbours don't anything the problems with rats on your property will continue."
Rats, which arrived in Australia by ship with the First Fleet have become endemic from the harbour's edge up to Oxford Street in Sydney's Darlinghurst and beyond.
In 2014, it was reported to a United Nations aged care conference that hordes of rats were "moving up the hill" as wharves were being knocked down for the Barangaroo harbourside development, and relocating to Millers Point where residents were using towels to barricade their bedrooms to keep them out.
But Prof Crowther said rats lived in every town and city in Australia, in relative density to human occupation and food supply.
"In Sydney you will see them around the parks at night, near the Harbour, in tunnels, around Central Station," he said.
"There's a localised population near the law building on the University of Sydney campus, wherever there's food and waste.
"They'll eat pet food and bird seed, protein fats and grains, if you leave that out."
Prof Crowther said rat predators included birds, cats and snakes, and that in less built up areas of Sydney large rat populations encouraged brown snakes, the world's second most venomous land snake.
"Rats are very destructive. They live for about two years and they will chew through anything.
"We haven't had a rat plague for a while. We have mice plagues mainly in the wheat belt area.
"In a plague they will eat more grain and reproduce with more and bigger litters, and eat and spoil our foods until the plague peaks and falls away, or they are poisoned."
Diseases spread by rats have included the rare infection rat lungwort, which can be fatal, and bubonic plague, which was brought to Australia by a genuine rat plague in Sydney in the early 1900s.
But rats currently living in Australian cities do spread salmonella, E coli and leptospirosis, a bacterial disease causing lead to kidney damage, meningitis, liver failure and even death.
The diseases can be contracted through touching or ingesting rat urine and faeces.
Canadian researchers who studied rat droppings found bacteria that cause diarrhoea and intestinal diseases, and identified 18 new viruses which potentially can infect humans.
Dr Cadhla Firth, a CSIRO scientist who studies the behaviour of rats and other vector borne disease spreaders, said that the more dense urbanisation became, the humans living in them would have to deal with rats and other animals.
"The more we move into cities, the more we are going to have to start wrestling with the animals and bugs that live among us," Dr Firth said.
The City of Sydney said rats were "an ongoing issue across Sydney" and "evidence from the City's rat baiting program doesn't indicate any recent increase in rat numbers".
"However, it is not uncommon to see more rats in summer as people spend more time outdoors," a council spokesperson said.
"There's no accurate way to count the number of rats in the city.
"Winter is the most active time of year for rats feeding. Generally, rats will seek out food and water close to the nest or in familiar locations."
The council advised property owners to remove overgrown vegetation and accumulated rubbish which might attract vermin.
HOW TO REDUCE THE RISK OF RAT INFESTATION
● Do not leave out pet food or bird seed
● Don't leave rubbish outside in bags
● Store rubbish in metal or heavy plastic bins
● Remove piles of timber, old furniture or debris from backyards
● Patch or seal holes in your garage or basement and repair broken tiles and concrete.