President Pranab Mukherjee in his message said, "On the joyous occasion of Onam, I offer my warm felicitations and heartiest greetings to all my brothers and sisters belonging to Kerala."
He said the festival brings out the rich cultural heritage of Kerala in its best form and spirit.
"May this harvest festival instill in us the spirit of national integration and inspire us to work for further development of our country," Mukherjee said.
Vice President M Hamid Ansari said Onam plays an important role in uniting people.
He wished that the festival "may usher in peace, prosperity and happiness in the society and contribute in the nation's progress".