Fears are mounting that a TV transmitter could topple over after it caught fire.
A 300 metre exclusion zone has been put in place around the Bilsdale transmiting centre in the North York Moors following the fire which broke out on Tuesday.
Crews from across the region were sent to extinguish the blaze, the cause of which is still unknown.
North Yorkshire Fire and Rescue Service said it worked through "difficult conditions" to stop the fire which left hundreds of homes across North Yorkshire without TV reception.
YorkshireLive reports that members of the public have been asked to keep away.
The fire service added: "Only one building in a complex of four was affected and there are concerns about the structural integrity of the mast.
"A 300 metre exclusion zone has been put in place around the mast.
"Eight pumps from North Yorkshire Fire and Rescue Service attended the incident and firefighting has now ceased until the site has been confirmed as safe for further work."
NYFRS said it would be working on Wednesday with Arqiva, the site operators, "to bring the incident to a safe conclusion".
The fire service said: "This area has limited access and we need to be able to move vehicles and people around to help fight the fire."
The base of the Bilsdale signal mast on moorland above Helmsley caught fire on Tuesday afternoon.
The transmitter tower was built in 1969 and currently supplies digital TV signals to a large area of north-east England.
A spokesman for Arqiva said: "The fire at Bilsdale has caused damage to our equipment and we are currently unable to broadcast TV and radio services from this site.
"Bilsdale is under the control of the fire services. We apologise for the inconvenience."
Ron Needham, 71, and his wife Sue, 69, who were out on hiking on the moors on Tuesday afternoon, witnessed smoke coming off the TV transmitter.
The couple from Wakefield stopped for lunch at the base of the mast during their 10-11-mile hike and noticed "nothing untoward at that stage", Mr Needham said.
Picking up their route along Cow Ridge, the hikers were about a mile and a half away when they glanced back at the mast at about 1.15pm.
"There was smoke coming out of the top a bit like a chimney," Mr Needham said. The couple sat and watched the smoke until they saw "a huge black cloud of smoke come from the buildings at the bottom".
Mr Needham said the sight left them "a little bit worried", adding that the mast "is almost a friend of ours", with the couple hiking the same route two or three times a year. It's something that you see from all over the moors, a bit of a landmark," he said.
"By the time we left the moor and got back down to our car along a narrow moorland road the smoke had stopped, so we assumed it was under control and then a fire engine came flying down this narrow moorland road."
Mr Needham added: "The initial thoughts were that it was something of a disaster."
The mast is primarily used for radio and television transmission and is among the most powerful in the UK.
It provides signals to parts of North Yorkshire and across the North East.
