Firefighters try to save one of world's tallest trees

Firefighters are trying to save one of the world's tallest non-redwood trees which mysteriously caught fire at the weekend.

The 325-foot (99 metres) Douglas Fir, known as the Doerner Fir, in Coos County Oregon, is still burning within the trunk.

Estimated to be around 450 years old, it has been burning since Saturday near the top of the tree.

Authorities are still investigating how the fire happened.

A main challenge in tackling the fire is where it is located within the tree.

While firefighters have managed to stop the fire on tree's canopy - its branches and leaves - there is a fire still burning inside the trunk.

An infrared drone flight showed that one area of heat is about 280 feet up the trunk.

This is where a fire is burning - inside the trunk itself.

Sprinklers have been placed at the bottom of the trunk, while helicopter teams were able to drop water from buckets on the leaf canopy above.

But due to safety concerns fire managers have said climbing crews will not be used.

Debris from the treetop has also made it unsafe for crews to work directly under the tree with the risk of falling parts of the treetop making it dangerous for crews to work directly under the tree

Doerner Fir is one of the largest coastal Douglas Fir trees in the world, and is estimated to be between 450 and 500 years old. It is one of the largest non-redwood trees.

How the tree caught fire is still a mystery.

Investigators from the Bureau of Land Management are working find out the cause, but have ruled out lightening after looking at weather data.