At least one person was killed and left six others injured after at least 18 speeding vehicles rammed into each other on the Agra-Noida Yamuna Expressway on Wednesday due to dense fog enveloping the national capital and adjoining areas. The accident, which took place due to low visibility, occurred at around 6:30 am near milestone 125, near Hataura village today. The video of the incident is doing the rounds on the social media. The Times of India quoted circle officer of Mahavan, DSP Alok Dubey, said, "One was killed and six people were injured. All injured have been sent to district government hospital for treatment. The deceased is yet to be identified." Station officer GP Singh of Mahavan police jurisdiction, meanwhile, said, "The trigger of the accident was a defunct car which was rammed from behind by a speeding truck. The truck was ferrying apple cartons and it turn-turtle after the collision. Since it was heavily dense morning, over a dozen of cars and heavy trucks kept on piling up on each other in back to back collision." The incident led to huge traffic jam on Yamuna Expressway. The national capital and its adjoining suburbs were blanketed in a grey haze this morning, dipping visibility to 300 meters at some places, causing train delays and slowing down flight operations. Some 30 trains coming to Delhi and 30 flights landing or taking off from the Delhi airport were delayed, according to officials. Poor visibility also caused heavy traffic snarls at many places in Delhi and NCR. The saving grace was the absence of hundreds of school buses on the roads. The situation is likely to worsen on Thursday as the weather department predicted "dense to very dense fog very likely" at many places in Punjab, Haryana, Chandigarh, Delhi, Rajasthan and western Uttar Pradesh.