The voting began at 7 AM at over 11,500 polling stations out of which 327 have been declared critical and 90 hyper critical.
A total of 1.27 crore voters are eligible to exercise their franchise which include over 3.37 lakh first-timers. A total of 150 candidates are in the fray.
The Congress had won all seven seats in the 2009 Lok Sabha polls.
The prominent contenders in the fray include Union Ministers Kapil Sibal and Krishna Tirath, Delhi BJP Chief Harsh Vardhan, Congress General Secretary Ajay Maken, journalist-turned-politician Ashutosh, Sandeep Dikshit, grandson of Mahatma Gandhi, Rajmohan Gandhi, and BJP's Meenakshi Lekhi.
Nearly 50,000 security personnel, apart from 161 flying squads of police and video surveillance teams have been deployed as part of arrangements to ensure fair and peaceful polls.
In a bid to boost voter turnout, a number of 'model' polling stations with spruced-up infrastructure have been set up for the first time.
In 2009 Lok Sabha polls, the overall voting percentage stood at 52.3 per cent, which increased to 66 per cent in the 2013 Delhi assembly election.
Delhi's Chief Electoral Officer Vijay Dev has said he was hopeful of even a better polling percentage in this election and appealed to Delhi voters to come out and vote.
The entry of Arvind Kejriwal-led AAP has changed the dimension of the elections as almost all constituencies are likely to witness a three-cornered fight.
For AAP, the election assumes a greater significance as it will be an acid test for the new party's perceived erosion of support base.
AAP created history in the December 4 assembly polls here, wresting 28 of the 70 seats and formed the government.
Kejriwal had faced severe criticism for quiting from the government after remaining in power for 49 days. Both Congress and BJP had mounted a shrill attack on Kejriwal accusing him of running away from responsibilities.
BJP's campaign was centred around Narendra Modi and the election will determine whether the 'Modi wave' had any impact or not. If the party performs well, then it may press for early assembly polls. The BJP had won 31 seats in the assembly polls but refused to form the government.
After its massive defeat in the assembly polls in December last year, Congress through its campaign tried hard to win back support of the people through rallies and house-to-house contact programme.