Fire crews battling a vast moorland blaze in North Yorkshire have said they have been hampered by exploding World War Two bombs and tank shells.

Emergency services have been tackling the fire, which covers about 10 sq miles (25 sq km), on Langdale Moor, in the North York Moors National Park, since Monday 11 August.

The county’s chief fire officer Jonathan Dyson said part of the site had been a tank training ground in the 1940s and there had been more than 18 explosions as the fire had burned down through the peat to previously hidden explosives.

Mr Dyson said the fire service was treating the incident as a “significant wildfire” and had requested help from other services across England.

Mr Dyson said in some places crews had to adopt a “very defensive fire-fighting strategy” due to the unexploded bombs.

“As the peat continues to burn down it is finding the Word War Two ordnance and therefore exploding and we have now experienced over 18 ordinance explosions within key areas.”

Mr Dyson said up to the weekend they had made significant progress in managing and containing the fire but, with a change due to the wind and the temperature, the blaze had “more than doubled in 24 hours”.

“The fire has made a rapid spread further north and across to the north west,” he said.

Crews were trying to minimise the spread and had 10 appliances committed to the operation along with 60 firefighters, he explained.

“I have today made a request to National Resilience for national assets to be deployed to the area.”

Mr Dyson said the help would consist of up to 10 appliances from other fire services across England and was expected to arrive swiftly.