Many Northern Ireland students may have to wait for up to a week before they discover if they are going to university.
While thousands of teenagers were celebrating yesterday's A- level results, others now face a desperate scramble to secure a university place.
Students who miss out this year will have to reapply next year - and if they opt to study in England face £9,000 in annual tuition fees.
Latest Ucas figures show that 682,367 people across the UK have applied to start undergraduate university courses this autumn; of these 57.6% have been accepted so far.
Clearing is available to students who failed to meet the grades required for their first choice of university and their insurance offer, as well as those who declined all their offers or did not receive any.
Tony Gallagher, pro vice chancellor of Queen's, said the majority of their 3,700 undergraduate places would go to people who had chosen the university as their first preference.
Only 100 places will be available at Queen's through clearing but students face a wait of up to a week before knowing if they have definitely secured a place.
By 9am yesterday University of Ulster's admissions helpline had dealt with 206 calls and continued to take more than 100 calls an hour.
It advised students via Twitter that "we are very busy, please be patient and keep trying".
The university, which has campuses at Jordanstown, Belfast, Coleraine and Londonderry, has just 50 places available through clearing.
Some universities in the rest of the UK are already full and have closed their clearing helplines. Exam board chiefs are also preparing themselves for a large number of queries from students challenging the grades awarded for their A-levels.
Andrew Hall, chief executive of the AQA board, said he would be "really surprised" if there was no increase in the number of results queries received last year, because of the fight for university places.
A spokesman for Northern Ireland's main exams body, CCEA, said: "At this early stage our helpline is experiencing a normal pattern of calls and queries regarding our re-mark services. We have the resources in place to meet any increased demand.
"For students going to university we have a priority system in place to make sure inquiries are dealt with quickly.
"We actively encourage any student who is concerned about their result to discuss the option of requesting a remark with their teacher."
Last year 1,210 inquiries about CCEA A-level and GCSE grades resulted in a change, which equated to 0.5% of all grades awarded.
Queries could also come from students affected by errors in this summer's A-level papers.
Hundreds of Northern Ireland students were hit by mistakes in 6 AS/A Level papers.
The blunders ranged from wrong answers in a multiple choice paper to impossible questions and printing errors.