A worker has been killed in a wall collapse triggered by high winds at a building site in Sydney's northwest and another is fighting for life after being crushed in a similar incident.
The 30-year-old died after he was trapped under a brick wall at Carlingford shortly before 10am on Wednesday, police said.
The structure, which was under construction, was "blown over in the wind".
The Bureau of Meteorology recorded gusts of up to 72km/h on Wednesday morning at the nearby Olympic Park weather station, while Cabramurra saw gusts of 100 km/h.
Paramedics performed CPR on the man at the Carlingford site after he went into cardiac arrest, an ambulance spokesman told AAP.
Minutes earlier, workers desperately dug through rubble to find their trapped colleague.
At Kellyville, about 20 kilometres away, paramedics treated a young man for significant head injuries after he too was struck by a collapsing wall about 10am.
The 19-year-old was taken to Westmead Hospital in a critical condition.
"It's understood the construction worker was pulled unconscious by co-workers from underneath the pile of bricks which collapsed during highly windy conditions," authorities said.
SafeWork NSW has sent inspectors to both sites.
A severe weather warning has been issued for vigorous winds in south-east New South Wales, particularly for people in Illawarra and parts of the South Coast, Central Tablelands, Southern Tablelands, Snowy Mountains and Australian Capital Territory Forecast Districts.
NSW State Emergency Service (SES) received almost 150 calls for help on Wednesday and was called to 112 jobs due to the strong winds.
The NSW Rural Fire Service (RFS) reported that the winds had fanned fires across the region, with the count at 70 bush and grass fires by the afternoon - 33 of those not yet under control.
