Rio de Janeiro and Chicago have emerged as the leading front-runners to win the vote when the International Olympic Committee (IOC) votes to pick a host city at its Session in Copenhagen on October 2.

But Coe warned that it would be premature to write off the two other challengers, Madrid and Tokyo.

The chairman of London 2012 said: "I think this is probably even closer and tighter than the 2012 round.

"I think we probably recognised at this stage in the 2012 round that London and Paris probably had the momentum, and you could probably at that point have looked at the other cities and said at least two of them are beginning to tread water.

"It's very difficult to say that about any of these cities."

Paris were the overwhelming favourites going into the vote at the IOC Session in Singapore in July 2005 but were beaten 54-50 by London.

Coe said: "They [the 2016 bid cities] are all cities quite capable of staging extraordinary Games.

"All have very smart, very clear visions.

"This one [race] is probably posing many IOC members bigger questions than for some of the other rounds."

London's shock victory has been studied closely by all the four candidates but Coe warned that they must try up to come up with their own winning formula.

He said: "The one thing I do know from the bid we were involved in and having become a little bit of a student of these bids, there isn't a set template.

"No city should be sitting there saying, 'London did this, Sochi did that, or Paris did this.'

"You have to do what you absolutely genuinely think is intrinsically a part of your narrative.

"Trying to do something simply because another city did it is a dangerous route."