New Zealand has warned hikers and climbers to steer clear of a volcano in a national park whose jagged rock formations and eerie barren landscapes featured in the Lord of the Rings movies.

Quake and volcano monitoring service GNS Science raised the alert for Mount Ruapehu, in the North Island’s Tongariro national park, which last erupted in 2007.

“There are more signs of life at the volcano,” said volcanologist Brad Scott.

The landscape formed the backdrop for Mordor’s hissing wasteland in Peter Jackson’s Lord of the Rings trilogy.

The Lord of the Rings: Fellowship of the Ring. Photograph: Everett/REX Shutterstock

The department of conservation warned trekkers to stay out of the summit hazard zone, within 2km of the centre of Crater Lake.

“Recent visits to the volcano have confirmed an increase in the output of volcanic gas,” GNS Science said.

The temperature of the lake has risen from 25C to 46C since mid-April. The volcanic alert level has been lifted to “heightened unrest” from “moderate”.

Each year, thousands of people trek the Tongariro Crossing, a 20km (12-mile) alpine crossing that passes all three volcanoes in the area.