Some labourers saw a burning stick being thrown by two men on a motorcycle.
"Some labourers were setting up tents near the entrance of the auditorium, where Prime Minister Manmohan Singh and Congress president Sonia Gandhi along with all senior party leaders will attend the party's Chintan Shivir, when they saw the two men," a police official told IANS.
The bike-borne men fled immediately.
"The tent went up in flames. With help of labourers, the fire was controlled within minutes," said the officer.
An investigation has been launched into the incident.
"Prima-facie, it seems the miscreants were in an inebriated state. We have ordered a probe into whether it was a pre-planned and intentional act," said the official.
Security has been stepped up inside and outside the Birla Auditorim, he added.
Aimed at paving the way for the return of the Congress-led United Progresive Alliance for a third consecutive term in 2014, the Chintan Shivir is scheduled to take place from Jan 18-20 here.
The conclave is expected to draw a roadmap for the party to counter the BJP in the assembly polls and the Lok Sabha elections.