The incident happened in the Ghatkopar area of the country's financial capital of Mumbai, Xinhua reported.
Videos on social media showed the huge billboard fell, trapping many cars and other vehicles under it. The billboard was installed next to a fuel station. The victims were taking shelter at the fuel station amid storm and rains when the mishap occurred.
Local police and the fire department workers rescued the people from underneath the billboard. They were later rushed to a local hospital.
According to latest reports, the Mumbai Police registered a criminal case against the owner of the billboard which was installed illegally.