Counting in the European election will resume in Northern Ireland on Tuesday with officials facing heavy criticism over the length of time the process has taken.

One MP branded Monday's 15-hour count a "disgrace and a complete shambles" after it was suspended just before 1am with only one of three candidates having been declared elected.

Sinn Féin's Martina Anderson emerged victorious after the first round of counting but further stages under the single transferable vote method failed to identify the other winners and the remaining candidates were left to await their fate overnight.

Democratic Unionist Diane Dodds is also likely to be re-elected after gaining more than 131,000 first preferences,. The third incumbent MEP, Jim Nicholson of the Ulster Unionists, is favourite to secure the other of the two vacant seats but is facing competition from the SDLP's Alex Attwood and the Traditional Unionist Voice's Jim Allister.

Dodds' husband Nigel, who is North Belfast MP and DUP deputy leader, was scathing of the Electoral Office for Northern Ireland, which was also criticised after delays plagued the 2011 assembly election count.

"I think it is a disgrace that once again the Electoral Office has operated things here at a count which has made Northern Ireland look a complete shambles in terms of counting votes," he said.

"There is absolutely no reason under the sun this shouldn't be done and dusted long before now and completed and the fact is, it seems to me, the Electoral Office simply hasn't put on enough staff. They never seem to do that.

"There is frustration amongst all parties about just how long this is taking and about the fact everywhere else in Europe has finished a long, long time ago and I just can't believe that we are once again in this situation in a Northern Ireland election and I think it does diminish democracy. People are entitled to have these votes declared in a timely and efficient way and it really does bring us into disrepute when it doesn't happen."

Graham Shields, the chief electoral officer for Northern Ireland, said the particular way the count had developed, with the requirement to recount all Anderson's ballots in order to distribute her surplus, had not been anticipated. He insisted lack of counting staff was not the issue as 270 people had been employed.

"We knew we were here for a long day and we potentially expected to be here if we needed to be into the early hours of the morning, but I don't think anybody could have reasonably foreseen that a count would have run into two days, for 24 hours," he said.

Shields said the episode underlined the need for electronic vote counting in Northern Ireland. "The electronic counting process, in my opinion, is an absolute necessity for going forward because none of us want to be here for days on end," he said.

Anderson said: "I am very honoured and proud that almost 160,000 people throughout the north have voted for myself."

The former Stormont junior minister hailed her party's success as it was poised to take four seats across the island.

"For the first time every voter in Ireland is going to be represented by Sinn Féin," she said.

Sinn Féin president Gerry Adams was among those cheering his party colleague's victory. "It's a good day for Sinn Féin's but I also think it's a good day for the people of the island," he said.

"We will now hopefully have more conversations, more discussion, more debate about citizens' rights, about a united Ireland and about the peace process."