Firefighters have been working through the night to bring a large moorland blaze under control.
West Yorkshire Fire and Rescue Service (WYFRS) said several acres of Ilkley Moor caught fire on Saturday after a day of soaring temperatures.
The fire involves moorland above White Wells in Ilkley. Bradford Council is warning walkers to keep off the moors.
Crews from 10 engines remained at the scene of the blaze overnight to damp down.
Originally there were 14 crews at the scene but WYFRS said it had scaled back its response to the blaze.
Labour Party leader Jeremy Corbyn said the "awful scenes" on the moor were a reminder "of why we urgently need to tackle climate change".
On Saturday night Martyn Hughes, a watch manager at North Yorkshire Fire and Rescue Service which is assisting WYFRS, tweeted: "The intense heat, steep slopes and rough terrain are causing the fire to spread rapidly whilst we try to get near the flames."
The Met Office confirmed Saturday was the hottest day of the year, with 25.5C recorded in Gosport, Hampshire.
Forecasters have said the UK is set for record-breaking temperatures over the rest of the Easter weekend.
In June and July last year, firefighters from 20 different brigades were drafted in to help tackle two huge moorland fires which burnt for several weeks.
Crews spent more than a month battling a huge fire covering 18km sq (6.9 sq miles) at Winter Hill, near Bolton.
The Army was drafted in to help Greater Manchester crews deal with a blaze at Saddleworth Moor in Tameside, 30 miles away from Winter Hill.