Embers ignite into dangerous grassfire during 9NEWS live cross

A 9NEWS report from an unfolding bushfire emergency has shown just how quickly a few embers can escalate into a dangerous grassfire.

Airlie Walsh was reporting from Londonderry in Sydney's west when a small spotfire started just off camera.

In less than a minute and as Walsh's report continued, the flames began to build, quickly reaching five metres into the air and licking at tree tops.

NSW Rural Fire Service firefighters quickly approached the spotfire and brought it under control.

Walsh said considering the fire that sprang up behind her was only a spotfire ahead of the man fire front, it was "pretty frightening to think this isn't even the worst of it". 

"It's hot, it's about 30 degrees. We can't see more than 10 metres in front of us," she said.

READ MORE: Homes under threat as out-of-control bushfire burns at Londonderry, west of Sydney