UPDATE: A 13-year-old boy has been charged with arson over the Mackay toy store fire.

He is due to appear in court in Mackay on Monday.

EARLIER:

FOUR juveniles, including two boys aged 10 and 13, have assisted police with their inquiries into a massive fire that gutted a shopping complex in Mackay today.

Police say the 10 and 13-year-old boys are still assisting them with "ongoing investigations".

The enormous fire, which completely destroyed the Toys R Us, Clark Rubber and Autobarn stores, was put out about 3pm and firefighters were hosing down remanent flames.

No one was injured.

Much of North Mackay was in lockdown when an emergency situation was declared, causing major traffic chaos with local streets in gridlock.

At 4pm, police lifted the emergency situation and reopened all roads, but a public safety order is still in place because of police concerns about toxic smoke from burning chemicals in some of the shops.

Were you there? Did you witness the fire? Email pictures and news tips to pictorial@qnp.newsltd.com.au

A police spokeswoman confirmed four juveniles were in police custody in relation to the incident.

One is understood to be a 15-year-old girl.

The fire, first reported to police at around 11.45am, saw Toys'R'Us, Autobarn and Clark Rubber totally engulfed by flames and a huge smoke plume cover the area.

Up to ten fire crews were called to Greenfields Boulevard to fight the blaze, which continued burning for almost five hours after the first Triple-Zero call was made.

Busy Saturday trading at the Toys R Us Mackay saw a mass evacuation from the building, and at 1.20pm, the roof of the Toys R Us was reported to be caving in.

The Bruce Highway at Nebo and all surrounding streets were closed.

Motorists are advised to avoid the area.

More to come...