The BJP lost all five seats in the MCD byelections held in March of last year, including its traditional bastion of Shalimar Bagh, which it had previously won.
With thunderstorms and light rain, temperatures are predicted to dip from June 27.
The 1.3-km-long tunnel, which has facilitated travel between downtown Delhi and the nearby satellite cities of Noida and Ghaziabad, has become a popular spot for taking selfies.