Image caption Bats with White-nose syndrome exhibit odd behaviour such as flying outside during the day

At least 5.7 million bats across 16 US states and Canada have died from White-nose syndrome, scientists studying the fungal ailment say.

The disease was first detected in a cave in New York state in 2006.

Previously, the US Fish and Wildlife Service closed caves and mines in an effort to hamper the spread of the disease.

Officials say bats provide value to the US economy as natural pest control in farms.

The nocturnal creatures also help to control insects that can spread disease to humans.

Bats with White-nose syndrome exhibit odd behaviour during the winter months, including flying outside during the day.

The rapid spread of the disease has also challenged officials' population estimates.

"White-nose syndrome has spread quickly through bat populations in eastern North America, and has caused significant mortality in many colonies," US national White-nose syndrome co-ordinator Dr Jeremy Coleman said in a statement.

"Many bats were lost before we were able to establish pre-White-nose syndrome population estimates."