Figures from the 'Yes' campaign suggest that 51.4% of voters who expressed a clear view support the package, with 48.6% opposed.
However, 26.8%, over a quarter of the electorate, are still to make up their minds.
On a District by District basis, the results are similarly tight.
Should these returns be accurate, the referendum would be lost, as only six of the Greater Manchester authorities would vote for the referendum, and at least seven are required.
Returns indicate that turn out is likely to exceed 63%.
The canvass, of 5003 residents of Greater Manchester, was conducted face to face and on the telephone between 27 October and 20 November.
Yes Campaign Director Dan Hodges said: "This referendum is on a knife edge. It's clear that in every district every single vote is going to count, and every single voter has the potential to make the vital difference.
"When this referendum was called the 'No' campaign thought victory was in the bag. I've got a sneaking suspicion that when all the ballots have been counted they’re going to come to regret taking the people of Greater Manchester for granted."