Over 70 trains were running behind schedule and 15 were cancelled due to dense fog, said a statement from the Indian Railways.
According to the India Meteorological Department (IMD), the temperature had last plummetted to such a low in 2008.
Similar conditions are expected on Monday.
The maximum temperature also went down nine notches below average at 11.8 degrees.
"There is no respite from the cold even now. I have not seen such harsh winter season in so many years," said Pallavi Batra, a housewife in south Delhi's Sarvodaya Enclave.
The homeless are having a harrowing time coping with the biting cold over the past few days. Residents of Lajpat Nagar donated woollens and blankets to the poor in the area.
Earlier on Sunday, fog enveloped the city in the morning with visibility dropping to 400 metres at 8.30 a.m., but it lifted in about two hours.
"There will be fog Monday morning but the sky will be clear during the day. The maximum and minimum temperatures are likely to be around 14 and 3 degrees Celsius, respectively," said an IMD official.