The DUP is talking up its role as kingmakers in the new Parliament after the Conservatives’ hopes of an election landslide appeared dashed.
An exit poll suggested the DUP may hold the balance of power in the new-look House of Commons.
Party leader Arlene Foster said her party had enjoyed a “very good night”.
In one of the biggest upsets, Ulster Unionist Danny Kinahan lost his set to the DUP’s Paul Girvan in South Antrim, who had a 3,208 majority.
In Foyle, Sinn Fein took the long-held SDLP seat from Mark Durkan.
Such a result represents a seismic shift in the power dynamic between the rival nationalist andn republican parties.
Independent Lady Sylvia Hermon was the first Northern Ireland MP to be elected just after 1.10am this morning although her majority of 9,202 was slashed to 1,200.
She was closely followed by Jim Shannon (DUP) in Strangford, returned in Strangford with an increased majority of 18,343.
Gregory Campbell (DUP) was comfortably returned in East Londonderry, as was Sinn Fein’s Paul Maskey in West Belfast.
Mr Maskey said his 27,101 tally was the highest Sinn Fein vote in the constituency.
Alliance leader Naomi Long conceded defeat to the DUP’s Gavin Robinson in East Belfast before a result was declared.
Turnout in most constituencies was very close to the figures in the March Assembly election, and up on the 2015 Westminster election.
On a dismal night for the SDLP and UUP, the DUP and Sinn Fein were poised to be the big winners.
Asked how many seats she believed the DUP would win overall, Mrs Foster said: “I don’t want to predict yet but we are very pleased with the way things are going at present.”
She added: “We fought this election on the importance of the Union and I think people really responded to that. It’s going to be a good night for the Union.”
Ian Paisley said if the exit poll suggesting a poor Conservative performance proved accurate it would put his party’s MPs in the position of “kingmakers” on crunch Brexit votes and other issues.
Looking comfortable in North Antrim, Mr Paisley insisted his party would not support a Jeremy Corbyn-led Labour party given his past associations with Sinn Fein.
“Anyone who thought that Northern Ireland’s voice was being lost in these talks I think tonight they are eating those words, under this set of circumstances — if that pertains — Northern Ireland unionist MPs would be the kingmaker on Brexit deals.
His party colleague Sir Jeffrey Donaldson, who was also returned in Lagan Valley with a thumping 20,000 majority, added: “In a hung Parliament scenario, assuming Conservatives are the largest party, of course we will talk to them about their desire to form a government.
“We are not going to make a prediction or set out in advance what our negotiating position will be because we don’t know at this stage what the scenario is.”
As the new make-up of Parliament became clear, Sinn Fein was facing renewed pressure to re-think its abstentionist policy.
A senior DUP source said: “Sinn Fein have now lost the influence they were seeking. On first impressions it looks like the tables have been turned on them.”
The poll put a combined Labour, Scottish Nationalist and Liberal Democrat vote at 314 seats — exactly the same as the Conservatives.
Arriving at the Belfast count, Sinn Fein president Gerry Adams ruled out the possibility of the party changing its abstentionist policy as a result of a hung Parliament scenario.
Mr Adams said the DUP always tended to “play up” the potential of hung Parliament situations and added: “I don’t know how Theresa May can survive this.”
Party colleague Francie Molloy warned it would make no change to Sinn Fein’s abstentionist policy, adding: “It would be a backward step if the DUP were to get concessions from a Conservative government.”
In North Down turnout was 61% — up slightly from 59.2% in March, and 56.1% two years ago in the last General Election.
In East Belfast, turnout was 67.7% — up from 63.0% in both the Assembly election and last Westminster poll.
South Antrim saw 64.4% turn out to vote — a rise from the March figure of 62.4% and 54.5% in 2015.