An Ipsos-Mori poll found 53 per cent of voters planned to vote No, while 47 per cent said they would vote Yes, after excluding undecided voters.
A YouGov survey found 52 per cent of Scots were to vote for the union with 48 per cent favouring independence, when undecided voters were excluded.
The result was mirrored in a Panelbase survey which also found 52 per cent of Scots backed the union compared with 48 per cent for independence, again with undecided voters excluded.
Across Scotland many polling stations saw record turnouts, with many expecting 80 per cent or higher.
As voters went to cast their ballot a Panelbase survey revealed just one in 20 of them still had to make up their mind.
It added that men continued to be more likely to support Scotland leaving the UK, with about 54 per cent said to be Yes voters, 44 per cent who were voting No and three per cent who were undecided.
And as voters turned out, bookmakers were turning their back on the Yes campaigning, with odds of independence going from 7/2 to 5/1, according to betting site matchbook.com.
Ladbrooks said that some £30,000 an hour had been spent on the referendum result since voting started.
Polls opened at 7am yesterday and voting numbers at several locations across Scotland were said to be at record levels, with campaigners in Inverness reporting queues before polling stations had even opened.
Scenes of widespread engagement were, however, marred by some ugly incidents.
Police reported a 44-year-old man was arrested at a Clydebank after confronting a No voter at a polling station.
Officers said an alleged assault happened in Faifley Road in Clydebank, West Dunbartonshire, at about 8.30am .
In Glasgow police were called to another incident when a 67-year-old woman was alleged to have assaulted another woman.
A spokesman for Police Scotland said: “Police Scotland can confirm that a 61-year-old woman has been arrested and charged with an alleged assault on a female in an incident at the Shettleston Community centre in Amulree Street, Glasgow at around 1pm.”
And voters turning up at a parish church doubling as a polling station near Loch Lomond found pro-independence vandals had spray-painted threatening graffiti onto the walls, telling people to “vote yes, or else”. The writing was quickly painted over by officials.
Elsewhere though, referendum Day was a scene of good natured rivalry. It also marked the first time 16 and 17-year-olds were able to vote, many doing so in their school uniform.
Electoral Commission figures showed around 90 percent of teenage voters had registered to have their say.