Gurugram, Dec. 16 -- Dense to very dense fog across south Haryana on Monday morning triggered multiple fatal accidents and major highway pile-ups, leaving at least four people dead and more than 30 injured, while Gurugram witnessed traffic chaos and several non-fatal crashes as visibility dropped to as low as 10 metres. The most severe incident took place around 7.30am on the Delhi-Mumbai Expressway in Nuh, where at least 18 vehicles were involved in a massive pile-up, police said. A senior NHAI official said, "Another dumper truck loaded with guavas toppled after hitting the mangled car and then rammed into a bitumen-laden truck. Within 15 minutes, nearly 18 vehicles had collided, as visibility was barely 10-15 metres." The chain reaction began when a bus rammed a dumper truck, followed by successive collisions. Two people died on the spot: CISF inspector Harish Sharma, 46, from Alwar; and Sheikh Mohammad Khalil, 44, a Jaipur-based businessman. Over 30 were injured, one critically. Police said an FIR will be registered against the unidentified truck driver who stopped first. Barely two kilometres ahead, another four-vehicle pile-up occurred under similar conditions, with no fatalities. In a separate incident in Faridabad, two men were killed when a Ford Endeavour rammed an illegally parked container truck on the DND-Faridabad flyway between 7.30am and 8am. The deceased were Vishal Kumar, 31, and his driver Sandeep Kumar, 24, both from Jaipur. A friend, Harsh, 25, was critically injured. Police said visibility was less than 10 metres. Gurugram reported three fog-related accidents on Southern Peripheral Road, Golf Course Extension Road and the KMP Expressway, with no fatalities. Dense fog caused heavy congestion on key routes, forcing many to start late or work from home. Sunil Sareen, joint convener of DXP-GDA, said, "There was hardly 20 metres of visibility on the expressway. Drivers were guessing lanes, which made driving extremely risky." Deputy commissioner of police (Traffic - Gurugram) Rajesh Mohan said police anticipated the conditions and deployed teams early. "We studied black spots and placed tyres at diversions and road conversions to slow vehicles and prevent sudden lane-cutting. Additional barricades were also installed at accident-prone stretches," DCP Mohan said. According to traffic police officials, visibility fell below 50 metres at several stretches, prompting deployment at key intersections like Signature Tower and IFFCO Chowk. The India Meteorological Department warned dense to very dense fog is likely to persist in isolated areas of Haryana, including Gurugram, Faridabad, Nuh, and Palwal. Gurugram recorded a maximum temperature of 22.9degC and a minimum of 8.3degC on Monday. Traffic police officials, meanwhile, urged motorists to use fog lamps, avoid overtaking, and maintain safe distances, with patrolling units instructed to monitor high-speed corridors continuously. A senior IMD official said that visibility across Gurugram is expected to fall below 1,000 metres during early morning and late-night hours throughout the week....