A raging wildfire engulfed fields as farmers use burning to clear their waste crops in Thailand.

Footage shows the massive inferno razing crops and grassland next to a barn on the side of the road in Phetchabun province on March 24.

Driver Ronnaphoom and his companions stopped by to watch the blaze.

He said: ‘We were driving home from the temple. It was frightening. I don't know what's the cause of the fire.'

Smoke from the fires in northern Thailand has caused toxic clouds of smog to engulf once-popular cities including Chiang Mai and Chiang Rai.

Residents and business owners in the region have called on local officials to declare the district a disaster zone. The designation will allow the rapid mobilisation of emergency resources.

However, both Chiang Rai governor Puttipong Sirimat and Interior Minister Anupong Paochinda refused, fearing the 'negative impact' of such labels.

Interior Minister Anupong added there was no clear PM2.5 dust threshold to declare a disaster because the pollution levels change constantly.

He said he has asked provincial governments to coordinate with the Ministry of Natural Resources and Environment to deal with the smog, which he said were mostly caused by forest fires in nature reserves.