Firefighters have warned that there could be more serious fires in the open caused by the hot weather and have urged members of the public to be vigilant.

Crews from Cambridgeshire helped tackle two field fires at Roxton, near St Neots, and a third at Warboys on Tuesday afternoon.

One of the Roxton fires involved 500 acres of standing crops and stubble and the second involved 100 acres, having spread from a combine harvester which caught fire. The Warboys fire also involved a blaze in a combine which spread to crops.

A spokesman for Cambridgeshire Fire and Rescue Service said: “In the continuing hot weather we anticipate there may be further incidents like these, so please remain vigilant and do what you can to help us prevent outdoor fires.”

Police had to close roads and householders were warned to keep their windows closed during the Roxton fires on the outskirts of St Neots from where a large plume of grey smoke could be seen.

Firefighters from St Neots joined Bedfordshire crews in tackling the fires, the first of which was reported just before 2pm and the second at 4.25pm.

Dozens of firefighters were involved in dealing with the two incidents.

A Bedfordshire fire service spokesman said: “Huge well done to all the crews involved and a special shout out to the local farmers who created a firebreak to ensure the fire did not spread and provided protection to nearby properties.”

Crews from Huntingdon, St Ives and Chatteris dealt with the combine harvester fire at Warboys where members of the farming community also made a firebreak to prevent the blaze spreading further.

Group Commander Kevin Napier, head of community fire safety at Cambridgeshire Fire and Rescue Service said: “Over the last few weeks, our combined fire control has received many calls relating to fires in the open in Cambridgeshire and Suffolk.

“These have ranged from forest fires to stack and crop fires. As we've seen with the moorland fires, these can quickly spread and burn for days, which require a significant amount of firefighting resources.”

He said: “We want to help ensure that people enjoy the sunny weather while it's here safely. High temperatures and dry areas of land can be perfect conditions for a fire to spread. Something as simple as not stubbing a cigarette out properly, or using a disposable barbecue on grass, can start a fire that can develop quickly.”

The fire service urged people to ensure cigarettes were completely out and not to throw them out of car windows, to put disposable barbecues on bricks and not on grass, not to leave glass bottles lying on the ground where the sun's rays passing through them can start a fire, not to leave campfires unattended and to talk to your children about the dangers of starting a fire.