AN ELDERLY farmer has been freed after he was trapped under a tractor in neck-deep water poisoned with toxic chemicals.

The tractor rolled into the water-filled ditch about noon today at a farm in Braemeadows, in north Queensland.

A Department of Community Safety spokeswoman said the tractor was carrying chemicals and they began seeping into the water the man was trapped in.

The man was freed about 3pm and paramedics are assessing his injuries.

Fire, ambulance and medical staff are at the scene and the Emergency Management Queensland helicopter flew in a paramedic and doctor.

A crane was also brought in to move the tractor.

An elderly lady, thought to be the man's wife, raised the alarm.