New Delhi, Dec. 30 -- Thick fog across the region early on Monday led to a significant drop in the visibility - 50 metres at both Safdarjung and Palam stations - thereby impacting both flight and train operations in the Capital. Over 550 flights were delayed, at least 130 cancelled and eight diverted at Delhi's Indira Gandhi International (IGI) airport on Monday. Dense to very dense fog is also expected in Punjab, Haryana, Chandigarh and west Uttar Pradesh during the same period - continuing to disrupt travel plans with more delays and cancellations likely. The India Meteorological department (IMD) issued red alert for dense fog on Tuesday. An airport official said that while the lowest visibility was 50 metres, the runway visual range (RVR) hovered between 125 and 175 metres between this period. For flights to land, the ideal visibility is 50 metres while 125 metres or higher visibility is required for the airplanes to take-off. This meant while departures were not on hold, operations were significantly disrupted till around 9am. An airport official said at least 130 flights were cancelled, with eight flights diverted to nearby airports too. Data from the flight tracking website FlightRadar24 showed over 550 flights were delayed, with an average delay time of around 27 minutes. Meteorological experts said that while the fog intensity may marginally reduce on Tuesday, dense fog is still likely during the early hours till January 1. "Wind speeds should increase a little on Tuesday so the fog intensity should be lower, but we are expecting dense fog on both Tuesday and Wednesday," said Mahesh Palawat, vice president at Skymet....