A pregnant woman stabbed multiple times in the stomach and chest after being confronted by an intruder in her Sydney home managed to stumble to her neighbours' house to get help.

Next-door neighbour Mark Bolger told reporters the woman managed to walk to his house after the incident about 8:30pm in Mount Colah in Sydney's north.

Neighbour Mark Bolger and his wife tried to comfort the woman. ( ABC News: Jade Macmillan )

"She just knocked on our door and said she'd been attacked and 'help me, help me'," Mr Bolger said.

"You could see blood but we couldn't see her actual wound."

Mr Bolger said the woman was so distressed she could barely speak while they waited for police to arrive.

"We put a blanket around her, my wife tried to comfort her and that's all we could do really," he said.

"We tried to move her inside the house but she was just so stressed out she didn't want to be moved from where she was."

The 33-year-old woman, who is several months pregnant, was at her home alone when the attack happened. She was stabbed several times in the abdomen and chest.

Plain-clothed police officers searching outside the home. ( ABC News )

NSW Ambulance Inspector Andrew Rienits said when paramedics arrived at the scene, the woman was in a critical condition.

"Paramedics that arrived first initially stabilised her, and with the assistance of a medical team from the NSW Ambulance rescue helicopter they transported her by road to hospital," he said.

"She was in a lot of pain. At this point in time we don't have any information about the unborn child itself."

It is understood the woman was also stabbed in her arm.

Her condition is listed as stable.

Neighbourhood 'in shock'

A trail of blood can be seen leading up to the home and a blanket and bloodied bandages remain on the front doorstep.

Forozah Farrae, who lives across the road, said the neighbourhood was in shock.

"I feel so sad. When I came home around ten o'clock last night I was really shocked, I couldn't drive I was just shaking," she said.

"I just keep praying for the lady ... We just keep hoping everything is going to be fine."

A 14-year-old boy was arrested at a home nearby about an hour after the attack.

He is being held at Hornsby Hospital, under police guard, waiting to undergo surgery for a hand wound.

A police spokeswoman said officers would speak to the boy once doctors had given him medical clearance.

The woman has requested that her medical condition and that of her baby be kept private.