The National Astronomical Research Institute of Thailand reported that the ground-level temperature hit negative 5 degrees Celsius at its observatory in the Doi Inthanon National Park in Chiang Mai on Thursday morning.
The institute reported on Facebook that officials at the observatory at the kilometre maker 44.4 in the park used a digital thermometer to measure the temperature at ground level in front of the observatory and found that the temperature dropped to negative 5C.
The institute said the area was also covered by frost.
A spokeswoman of the institute, Piriyaporn Sappasri, confirmed that the officials of the observatory recorded the minus 5C temperature, which was unprecedented.
She said the officials measured the temperature at 6.30am and took photos of frost to post on Facebook.