A decision to this effect was taken at a special meeting of the Union cabinet, which condoled the death of the anti-apartheid icon.
"Mandela was the tallest leader of not only his generation but possibly this entire paradigm. The role that he personally played in dismantling the apartheid is something exemplary," Information and Broadcasting Minister Manish Tewari said after the meeting.
A prisoner of conscience for over 20 years, the South African leader played an extremely vital role in giving a moral leadership to the world, he said.
"The entire nation is one with the South African people in condoling his sad demise. The Cabinet met and passed a resolution condoling the death of Dr Nelson Mandela and it has been decided that there would be five days' state mourning," he said.
During the period of state mourning beginning on Friday, the national flag will be flown at half-mast all over the country and there will be no official entertainment.
The state mourning will be observed till December 10, a government notification said.