Hundreds of party workers thronged the Congress office amid bursting of firecrackers and beating of drums.
Several leaders, including Anand Sharma, Randeep Surjewala and RPN Singh, joined party workers in the celebrations.
Meanwhile, a continuous flow of enthused Congress workers and vehicles parked outside the party office caused a traffic jam on Akbar Road, which was later cleared by Delhi traffic police.
Some senior party leaders could be seen urging rapturous Congress workers to celebrate outside due to overcrowding in the office premises.
"Today's results have shown that (Prime Minister Narendra) Modi's fake popularity is declining and people do not want his party to form the government. This is just the beginning. The BJP will be destroyed in the coming times," Ajay Chikara, a Youth Congress leader, told IANS.
Earlier, addressing media persons in the afternoon at the party office, Congress vice president Rahul Gandhi termed the BJP defeat "a lesson for Prime Minister Modi".
"Modi-ji should now understand that dividing people on the basis of religion won't work. This country is for everyone and everyone has the right to stay here," he said.
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