The first day of ticket sales for the 2012 London Olympics was going "very well", Games organisers have said.
People have until 26 April to apply for some of the 6.6 million tickets which went on sale 500 days before the event.
But London 2012 chairman Lord Coe has admitted only half of tickets for the opening ceremony and some major events would be available to the public.
Earlier there were red faces when the Olympic countdown clock in Trafalgar Square in central London stopped.
The 6.5m (21ft) high digital timepiece became stuck on 500 days and 7:06:56, less than 24 hours after being unveiled.
A spokesman for watchmaker the Swatch Group said: "We are obviously very disappointed that the clock has suffered this technical issue.
"The Omega London 2012 countdown clock was developed by our experts and fully tested ahead of the launch in Trafalgar Square.
"We are currently looking into why this happened and expect to have the clock functioning as normal as soon as possible."
On ticket sales, London 2012 chairman Lord Coe said: "The reports are good. We went online early hours of the morning, ticket sales have been steady - which is what we wanted - and no reports of anything untoward.
"So, good, so far - let's keep our fingers crossed."
But when asked what proportion of the tickets would be available to the public for high-profile events he told BBC London: "We're still working through it but... it is probably more likely to be 50% for the 100m final or the opening ceremony."
Corporate clients and VIPs have often had special access to big nights in the Games.
Ticket prices for the public range from £20 to £2,012 and oversubscribed events will be decided by a ballot.
Several events will be free, such as the marathon, and 2.5 million tickets will be available for £20 and under. Others start at between £30 and £50. Half a billion pounds is forecast to be raised from ticket sales.
Organisers said they were confident they had done everything they could to avoid the website crashing as people logged on for the first time to buy tickets.
The main factor is the establishment of a 42-day sales process which means each application until 26 April will be treated in exactly the same way.
People can also apply using a paper form, obtainable from branches of Lloyds TSB, Bank of Scotland in Scotland and libraries in Northern Ireland, until 25 April.
Children under 17 will be able to "pay-your-age" to see some of the early heats, while the over-60s can watch for £16 at the same events.
Some 75% - or 6.6 million - of the 8.8 million Games tickets are available to the general public via the application process.
Of the remaining 2.2 million tickets, roughly half will be issued to National Olympic Committees (NOC) of each country, and half will be split between sponsors, the IOC, guests and hospitality partners.
People from some European countries can apply through the London 2012 website but residents of other countries can apply through their National Olympic Committee or appointed authorised ticket reseller.
A further two million tickets for the Paralympic Games go on sale on 9 September.
The London Organising Committee (Locog) has faced calls from the London Assembly for a record of all tickets reserved for officials, politicians and VIPs to be published.
Organisers still cannot say exactly how many seats will be available to the public for the big events in the Olympic stadium such as the opening ceremony and the 100 metres final, other than the figure will be more than 50% of the tickets available.
Lord Coe said he was confident the Games would be a sellout.
When the website did open, people applying for tickets found the site could not process their order if their Visa card expires before August.
Visa said in a statement: "Visa cards with an expiry date before August 2011 are not currently being accepted on the London 2012 ticketing website.
"We are working with all relevant parties to resolve this as soon as possible and will make a further announcement shortly. We apologise for any inconvenience this may cause.
"Tickets are not issued on a first-come, first-served basis, and any ticket registration taking place by 26 April 2011 will have an equal chance of success in the ballot."
Ten councils in London have decided not to accept an offer to buy up to 100 Olympics tickets, mainly because they do not think it is the right use of public money.
They are Barking and Dagenham, Barnet, Bromley, Camden, Kingston, Croydon, Harrow, Havering, Redbridge and Westminster.
London 2012 said any tickets not taken up would be offered to the public.
There has been some criticism of the ticket-buying process as all online tickets can be paid for only with a Visa card.
Organisers said this was in recognition of Visa's sponsorship of the Games, but critics say it is unfair.
Visa Europe has said people who do not have a Visa debit or credit card and do not wish to get one can obtain a Visa prepaid card to purchase Olympic tickets.
Concerns have also been raised about payments made on Visa debit cards.
Locog said payment would be taken between 10 May and 10 June and people would be told by 24 June which events they had tickets for.
This could mean money going out of bank accounts before the buyer knows which tickets they are getting.
Efforts are being stepped up to curb ticket touting, with the government planning to raise the maximum penalty from £5,000 to £20,000.