A FUEL truck has exploded in flames and two people are dead after a horror crash on Sydney's northern beaches.

Several vehicles were involved in the crash and NSW fire authorities said several firefighter crews had been deployed to stop flames from spreading further.

At least five people were taken to hospital.

Photographer Tim Pascoe was early to the scene and captured these dramatic pictures and video of the truck ablaze.

Police said emergency services were called to the scene about 3.40pm after a collision on Mona Vale Road near Ponderosa Parade.

A nearby resident told ABC Radio it appeared the truck had "cleaned up" four or five cars and jackknifed. Another caller said there was fire up into the sky and black smoke.

Mona vale rd pic.twitter.com/g2SasGPvHe — Doug Fraser (@dug_fraser) October 1, 2013

Nearby buildings including Pittwater RSL Club have been evacuated and police have advised motorists to avoid the area. Mona Vale Road is closed.

Olivia Lane, who works at Aussie Home Loans in Mona Vale, described the scene as "just chaos".

"I just went up the road to have a sticky (beak). Mona Vale road is closed in both directions and the latest was that a tanker went through the roundabout on Samuel and flipped, and took out two cars," she told AAP.

"It's just chaos - traffic, black smoke, helicopters have just turned up. It's pretty crazy.

"I didn't hear it but I did see the smoke, and then I heard an explosion."

Ambulance NSW had 12 units on the scene and a spokeswoman said it is treating the crash at Mona Vale as a major incident.

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