Strong winds and thunderstorms across New South Wales were generating dangerous conditions for firefighters on Sunday evening as more homes were reported lost in the Bega Valley.

Cooler temperatures forecast for Monday and the chance of substantial rain was giving fire authorities hope that conditions would ease on the other side of a cool change in the weather.

On Sunday morning, NSW Health told residents in several parts of the state to restrict outdoor activities after bushfire smoke and dust caused air quality problems.

In the Bega Valley in south-eastern NSW, the 177,000-hectare Border fire pushed north late on Saturday, while three other blazes in the south-west had merged into one.

The Bega Valley shire council mayor, Kristy McBain, said on Sunday more than 400 properties and homes had been lost after 34 days of fire activity in her area.

An unconfirmed number of homes were lost in Wyndham and Tantawangalo in the latest blazes.

She said: “It’s hard for people because this has been going on for 34 days and counting. We had homes lost on day one and day 34 we are still losing homes.”

Late on Sunday afternoon there were still more than 60 fires burning across the state, with 30 not contained.

McBain said cooler weather gave some reprieve to the community on Sunday but a big south-westerly wind is expected on Monday, which residents fear will cause more problems for the area.

“Everyone is just catching their breath today before tomorrow afternoon it flares up again,” she said.

The NSW Rural Fire Service told Guardian Australia on Sunday evening it had received reports of property losses in Bega Valley, but they were unable to confirm the reports as conditions were not safe enough for building impact assessment teams to enter the area.

Thunderstorms breaking out in parts of NSW could create challenging conditions for Sunday evening, but there was some hope for better conditions on the other side of the cool change.

🌩️⚡⚡FAST MOVING GUSTY STORMS FOR EASTERN NSW. Severe #Thunderstorm Warning for Damaging Winds & Heavy Rainfall. Latest warnings at https://t.co/vrZOdcTJ9k. pic.twitter.com/7LwBsilcSI — Bureau of Meteorology, New South Wales (@BOM_NSW) February 2, 2020

The NSW RFS spokesperson Greg Allan said: “We are seeing areas with thunderstorm activity and that could make conditions on fire grounds erratic and dangerous.”

On Sunday afternoon, firefighters were working to control the Erskine Creek fire south of Wentworth Falls in the Blue Mountains.

But Allan said forecasts were for damaging winds over the same Erskine Creek area on Sunday evening.

“That will cause that fire ground to be very erratic. Conditions are still very dangerous even in the Bega Valley.

“For the next 24 hours, people still need to be very vigilant,” he said, adding people in bushfire-prone areas should continue to discuss their survival plans.

Allan added: “The forecast is looking much better for next week with some thunderstorms, but also a substantial amount of rain.”

NSW Health issued a warning on Sunday morning for smoke haze and dust from the blazes, with Sydney suffering poor air quality.

The department’s medical adviser, Dr Adi Vyas, said dust from dust storms in western NSW may affect western Sydney.

Residents were told to minimise their exposure to the conditions outside. People with chronic respiratory and cardiovascular conditions, asthma, chronic bronchitis, emphysema and heart disease were told to follow medical plans.

Even when air quality had improved, symptoms could persist for several days if dust and smoke had been inhaled.

She added: “Ongoing heatwave conditions means that we all need to take extra care over the coming days.”

In the ACT, the threat from the Orroral Valley fire eased. The fire wasn’t controlled yet, but authorities downgraded the threat to “advice” level as they waited for forecast storms that could either help or hinder conditions.