Colorado's High Park wildfire has passed the 100sq km mark, making it the worst in the state's history.

The fire, which was started by a lightning strike over two weeks ago, shows no signs of slowing down.

Thousands of homes have been evacuated and almost 200 destroyed near Fort Collins, killing a 62-year-old woman whose remains were found in a cabin.

Firefighters thought they had controlled the worst of the blaze as lowering temperatures and light winds helped them seal off 60 per cent of its perimeter.

However, a sudden increase in wind and heat on Saturday saw that slip to 45 per cent, giving the 68,000 acre blaze more room to grow.