Demand for Take That tickets has been "twice that of Michael Jackson."
Tickets to see the group when they tour the UK next year for the first time as a five-piece since 1995 went on sale this morning, but demand via phonelines and on the internet has seen ticket sellers struggle to cope.
A spokesperson for vendor Ticketmaster said: "Due to totally unprecedented demand all ticket agents across the UK are struggling to cope.
"It's been confirmed that the UK telephone network is also straining to cope and that call volume, and it is at least twice that of when Michael Jackson tickets went on sale last March.
"We are working to resolve the issues and we are confident that fans will be able to purchase tickets and we ask that they keep trying."
Michael Jackson announced his 50 date 'This Is It' comeback would be staged in London last year - the only shows he planned to play in the world - which sold out within hours. The shows never went ahead, however, due to the untimely death of the star.
Take That - including recently rejoined member Robbie Williams - have also announced extra dates in the UK as a result of fan demand, with an extra concert at Sunderland's Stadium of Light on Tuesday 31 May, 2011, as well as extra shows in Glasgow, at Hampden Park, on Friday June 24 and in Birmingham, at Villa Park, on Tuesday June 28.
Mobile phone network Orange reported it had a 144 per cent spike in calls between 9am and 10am as to the previous day, as its customers frantically tried to get tickets.
The network said Orange customers can stay updated with the latest Take That news by visiting www.orange.co.uk/monkey or download a Take That ringtone from Orangeworld.co.uk
Take That 'Progress Live 2011' tour dates:
May 30: Stadium of Light, Sunderland
May 31: Stadium of Light, Sunderland
June 3: City of Manchester Stadium, Manchester
June 4: City of Manchester Stadium, Manchester
June 5: City of Manchester Stadium, Manchester
June 7: City of Manchester Stadium, Manchester
June 14: Millennium Stadium, Cardiff
June 18: Croke Park, Dublin
June 22: Hampden Park, Glasgow
June 23: Hampden Park, Glasgow
June 24: Hampden Park, Glasgow
June 27: Villa Park, Birmingham
June 28: Villa Park, Birmingham
July 1: Wembley Stadium, London
July 2: Wembley Stadium, London
July 3: Wembley Stadium, London
July 5: Wembley Stadium, London
July 12: San Siro, Milan
July 16: Amsterdam Arena, Amsterdam
July 22: Imtech Arena, Hamburg
25 July: Espirit Arena, Dusseldorf
29 July: Olympiastadion, Munich