At least 36 people were injured in the collision, some of them seriously.
The vehicles had been sent out to assist in the work against the storm Alfred, which is currently sweeping in over Australia's east coast.
Alfred was originally a tropical cyclone, but was downgraded when it approached land. The storm's winds and heavy rainfall are still expected to hit Australian coastal communities hard. So far, one person has been confirmed dead, writes AP.
On Saturday, around 330,000 households are without power in the states of Queensland and New South Wales.
This is the largest power outage due to a natural disaster in Queensland's history, says State Minister David Crisafulli.
