A theatrical mixture of ancient and modern Greece launched the Athens Olympics on Friday, lifting spirits in the Games' birthplace after the host nation was rocked by a drugs drama involving its two top sprinters.

A worldwide television audience saw a grand opening ceremony lift the curtain on the biggest sports show on earth, as patrolling helicopters and troops underlined the Games are guarded by the largest security operation in peacetime Europe.

International Olympic Committee President (IOC) Jacques Rogge and Greek leaders have said everything humanly possible has been done to ensure the safety and success of the Olympics -- the first summer Games since the September 11, 2001 attacks.

Former U.S. President George Bush is in Greece to join world leaders in a show of unity behind the Olympic ideal of peace. Prime Minister Tayyip Erdogan of Greece's long-time rival Turkey has said he will bring a message of global cooperation.

Tens of thousands packed the futuristic new Olympic Stadium, centrepiece of a two-week festival of sport that was under threat from chaotic construction delays until the last minute.

A heartbeat of drums counted down to the opening moment and then, amid torchlight and fireworks, a boy aboard a paper boat drifted across the make-believe Aegean Sea waving a Greek flag.

Combining symbolism of the ancient Greece that created the Olympic Games nearly 3,000 years ago with 21st technology, giant sculptures appeared above the waters. A living frieze of Greek history paraded by, the voice of opera diva Maria Callas echoed across the stadium and lasers created a DNA helix.

Led by the Greek flag, athletes from the 202 competing nations then streamed in, with tiny Saint Lucia -- Agia Loukia in Greek -- taking alphabetical pride of place at their head.

MAJOR EMBARRASSMENT

Hours before the ceremony, the IOC spared host nation major embarrassment by granting "Greece Lightning" Costas Kenteris and Katerina Thanou more time to explain why they missed dope tests.

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But a 72-hour extension for Olympic 200 metres champion Kenteris and Thanou, 100 silver medallist, after they failed to show up for a disciplinary hearing on Friday was perhaps only a postponement of what could still turn into a national scandal.

The twists and turns of a drama in which the two were injured in a motorbike crash and ended up in hospital stunned Greece as television and radio stations broke into programmes with the latest news on the nation's heroes.

Officials said neither was seriously hurt but had been ordered to stay in medical care for at least two more days.

"In order to ensure a fair process and give due consideration to the athletes, the disciplinary commission has decided to postpone the hearing until Monday," the IOC said.

The Greek National Olympic Committee said it would hold a special meeting on Saturday to discuss the missed doping tests and "all relevant developments".

After waiting in vain for the pair to leave hospital for the hearing, IOC drugs panel member Sergei Bubka, the Ukrainian former Olympic pole vault champion, said: "It was a doctor's decision. It wasn't really our decision."

DAMOCLES

Deepening the murk of a case that may leave doubt hanging over the pair like the sword of Damocles, Bubka said: "It was there on a medical certificate. It said these athletes should not be transferred anywhere for 48 hours."

The sudden cloud of suspicion over Kenteris and Thanou delivered a severe shock to a country savouring one of its proudest moments.

World Anti-Doping Agency chairman Dick Pound eased anxieties a bit, saying the three-day delay was no big deal "because the athletics doesn't start until the second week anyway (and) this gives them more time to get all the information they need".

International Association of Athletics Federations general secretary Istvan Gyulai said Kenteris and Thanou both missed drugs tests in Chicago several days ago after leaving for Athens a day earlier than planned.

Rogge said the fact the two were Greek national heroes would have no bearing on their fate.

The three-member IOC disciplinary commission has the power to rule a missed test is a failed test, carrying a two-year ban.

A statement on their injuries in the crash, in which no other vehicle was involved, said Kenteris "sustained a slight head injury, a sprain to the vertebra at the back of his neck, a knee sprain and scratches to his right leg". Thanou suffered "slight abdominal injuries, a sprain to the right leg".

Greek Olympic team spokesman George Gakis said the pair were not out of the squad and sprint coach Christos Tzekos said the two could be fit in time to compete.

"They don't have a serious problem. We'll see over the next few days how their health develops," said Tzekos. The women's 100 metres final is on August 21, the men's 200 on August 26.

But all of Greece was staggered by the news. Call-in show reaction swung from sympathy to stoicism to paranoia.

The daily Ethnos newspaper urged the sprinters: "Tell us the truth -- You owe it to all Greeks to prove you are clean".