Fire in Germany's Harz mountains spreading underground

A major fire has spread underground in Germany's Harz region, a mountainous area popular with hikers, according to the local authorities.

"After evaluating the latest thermal images from the reconnaissance helicopter, the fire has spread to an area of 160 hectares," a spokesperson for the Harz district said on Tuesday.

According to an earlier report, the flames were under control in an area of 150 hectares.

The flames spread undetected underground, the spokesperson explained, but stressed that the fire was still under control.

A total of seven firefighting helicopters and two firefighting aircraft are currently battling the flames. The area is considered difficult to access.

On Wednesday, efforts to extinguish the flames will continue from the air, while firefighting crews on the ground will be intensified. According to the spokesperson, 300 emergency personnel were already fighting the fire.

The weather is expected to help from Wednesday, as the German Weather Service expects rain in the afternoon.

Authorities expect firefighting efforts to go on for several days.

The blaze was discovered on Saturday afternoon along the Goethe Way, or Goetheweg, one of the most popular hiking trails in the national park.

Water to fight the fire is to be taken from nearby Concordia Lake, which remains closed to visitors.

The spokesperson said that people who had come to watch firefighting efforts actually got in the crews' way, which he called "a bit difficult" for the emergency services.

District administrator Thomas Balcerowski declared a disaster early on Sunday.