Delhi, Jan 17 : Over 110 international and domestic flights were delayed while around 25 were cancelled in the last 10 hours as a thick layer of fog blanketed Delhi, as per airport sources. The weatherman said that the visibility at Palam dropped to 300 metres at around 11 p.m. on Tuesday, which continued over the night and at 8:30 a.m Wednesday it was 600 metres. The IMD classifies fog intensity into four types: shallow, moderate, dense and very dense fog. The visibility ranges from 999 m to 500 m, 499 m to 200 m, 199 m to 50 m and less than 50 m, respectively. 'Latest Satellite pictures at 0700 am of today indicates that fog has reduced over Bihar, east UP, north MP & Delhi since midnight. However, dense fog is still prevailing over parts of Punjab, Haryana, West Uttar Pradesh & northwest Rajasthan and likely to continue few more hours,' IMD said in a tweet at 8:30 a.m. /IANS