Media playback is unsupported on your device
31 July 2015 Last updated at 18:45 BST
They include those who have travelled north across the border.
BBC Ireland Correspondent Andy Martin reports.

The firm admitted releasing a quantity of benzole, exposing five workers to risk of death from flammable vapours coming off it, in June 2011.
A Health and Safety Executive (HSE) investigation showed it failed to take appropriate safety measures.
Tata Steel was fined £930,000 and ordered to pay costs of £70,000, at a hearing at Hull Crown Court.
At a previous hearing, the company pleaded guilty to breaching the Health and Safety at Work Act 1974.
More stories from around East Yorkshire and northern Lincolnshire
The HSE said two of the workers involved in the incident were exposed to the chemical and suffered coughing and breathing difficulties. They were sent to hospital and discharged the next day.
It said the release of benzole could have caused serious injury or death had it been ignited.
HSE inspector Stephen Hargreaves said: "It was extremely fortunate no one was seriously affected by this incident. Had the flammable vapour cloud ignited this could have resulted in multiple fatalities.
"This incident highlights the need for all duty holders to implement and address all concerns and potential risks which have been identified.
"Tata's failure to do so in this case put a number of workers at risk of serious harm."

The club's latest accounts, for the year ending May 2014, also show the Bluebirds owe around £174m - most of it to owner Vincent Tan.
This was despite revenue increasing more than five fold to almost £80m.
The club's annual report says support from Malaysian investors "will continue" as long as "the business develops as planned".
The financial figures showed that the club's broadcasting and commercial income rose from from £8m to more than £70m.
Wages and salaries went up from just over £27m to £46m.
During their time in the Premier League Cardiff sacked Malky Mackay and replaced him with Ole Gunnar Solskjaer.
The club said they paid just over £2m on "exceptional costs" relating to the change of football and senior management.
The accounts show the club received loans of around £130m - mainly from Tan, but also including a loan of £7.5m from Torman Finance, understood to be chairman Mehmet Dalman's company.
The report adds: "Following relegation from the Barclays Premier League the owners are aware that they needed to again invest in strengthening the playing squad, but that they needed to spend wisely.
"Whilst long term funding is not guaranteed, the Malaysian investors have indicated that providing the business develops as planned, they will continue to support the company in the foreseeable future and provide additional finances in order that it can settle its liabilities."
Tan has previously said he will convert the club's debt into equity.
Keith Morgan, a chartered accountant who sits on the board of Cardiff City Supporters Trust, told BBC Radio Wales Sport: "The club is highly insolvent.
"It has far more liabilities than assets and at any point in time it could be called upon to repay that debt owed to Vincent Tan."

The French duo, seeded seventh, beat Russian fifth seeds Ekaterina Makarova and Elena Vesnina 6-3 2-6 6-4.
Garcia and Mladenovic claimed their first Grand Slam title having only teamed up this year with a target of playing at the Olympics.
They have now won titles in Charleston, Stuttgart, Madrid and Paris.
Subscribe to the BBC Sport newsletter to get our pick of news, features and video sent to your inbox.
The BBC has learned that the number of illegal immigrants caught trying to get from Northern Ireland's ports to other parts of the UK has risen significantly.
[NEXT_CONCEPT]
Tata Steel has been ordered to pay £1m after it exposed five people to toxic substances at Scunthorpe Steel Works.
[NEXT_CONCEPT]
Cardiff City lost nearly £12m during their debut season in the Premier League.
[NEXT_CONCEPT]
Caroline Garcia and Kristina Mladenovic gave the Paris crowd a home victory to cheer as they won the women's doubles title at the French Open.