While people are still coming in late for work in Britain this morning, the millennium will already be arriving in Kiribati, in the furthest reaches of the South Pacific. From then until well into the next day, when the west coast of the US celebrates, computer systems around the world will be changing their dates, one after the other.
The first serious deadline occurs in New Zealand, the first developed nation to hit midnight, at 11am London time.Australia, which follows a couple of hours later, also has a high level of preparedness and few difficulties are expected.
But as midday arrives in London, the clocks chime for midnight in the furthest eastern reaches of Russia, the biggest uncertainty of all.
With Russian defence ministry specialists on joint vigil with US officers at Petersen Air Base, Colorado, the world is reasonably well insured against an accidental missile launch. But some Western experts worry about Russia's nuclear power stations, where the manual back-up systems will require extra human attention. Said one analyst: "Russians like to party at New Year and this country, as we know, is not at its strongest when it comes to safety culture."
As the afternoon wears on in Britain, Japan and Korea arrive at midnight. Japan started preparing for Y2K relatively late and the Prime Minister, Keizo Obuchi, is urging citizens to stockpile three days' food and water. But far more worrying is North Korea, a secluded, Stalinist nation with nuclear weapons and in severe economic difficulties.
As darkness falls across Britain, midnight strikes inChina. Responsibility for dealing with the millennium bug there rests with a vast range of organisations at national and local levels, and it is hard to predict how they will cope.
Indonesia is high on nearly every list of potential trouble- spots. There is potential for major disruption in power, medical care and especially in transport links, a crucial sector in the world's largest archipelago. The banking system is also vulnerable.
Before most people in Britain have begun partying, midnight will strike across south Asia, and most of the world's population will have crossed into the next millennium. Bangladesh and Sri Lanka may have some problems but these will be mitigated by the relatively low level of computerisation. India started working on Y2K very late. Again, power, banking and transport are the sectors expected to see the biggest problems.
Pakistan's prospects are far worse. Preventive action came to a grinding halt after the coup on 12 October. Now the airports, hospitals and power stations are feared to be unready.
As the parties in Britain are starting to get under way, another huge chunk of the world moves into the new century, including western Russia, central Europe, much of the Middle East and east Africa.
Central and eastern Europe, caught between capitalism and communism, are key cause of concern. Some state-run monopolies supplying water and electricity could be hit, although new computer systems have been installed by Western investors.
In most African countriespeople do not rely heavily on technology. None the less, nervy businesses and investors have stayed away, even from South Africa. Israel, which has a booming hi-tech industry, considers itself one of the best prepared countries, though outside observers are less confident. Elsewhere in the Middle East, the picture is patchy. The US State Department predicts potential disruption in power and telecommunications in Saudi Arabia and Qatar.
One hour before midnight in London, the rest of western Europe hits the New Year. The region is not expected to experience any serious difficulties. Several European organisations will be gathering information, including Nato and the Swift financial communications network linking banks, stock markets, securities and clearing houses. The European Commission is deploying specialists, including some in nuclear energy.
When the millennium finally comes to London it also comes to the millions of computer systems around the world that use Universal Coordinated Time (UTC), which is the same as GMT.
Despite assurances, no one quite believes there is an effective Y2K bug repellent in Latin America. Mexico is regarded as being well-prepared, but parts of South America - much of it in recession - may not fare so well.
The biggest test of the yearwill come almost last: the United States, the world's most technically dependent country and the place responsible for the Y2K bug. Concerns centre on the banking industry.
The Federal Reserve is opening a war room to monitor computer problems, and is holding an extra $50bn (pounds 30bn) in its vaults to distribute to any institutions that may be drained of funds. There will probably also be localised problems with electricity, water, gas and telecommunications.