Thousands of people are feared dead after two hijacked aircraft destroyed New York's World Trade Centre in the worst terrorist attack of all time.

The whole of America was gripped by terror after the suicide bombers struck with devastating deadliness.

Sky News reported an "Armageddon" scenario after an aircraft ploughed into the industrial city of Pittsburgh in Pennsylvania.

It came down less than two hours after two jets were deliberately flown kamikaze-style into the World Trade Centre, one of the world's most famous buildings.

American Airlines said they'd lost two aircraft with the loss of 156 passengers.

Both the centre's South and North Towers simply imploded after the steel structure was melted by the lethal impact of the blazing aircraft.

New York mayor Rudolph Giuliani said a "tremendous number of lives had been lost".

The UK was also put on full alert.

The Canary Wharf centre, the tallest building in Britain, and Stock Exchange in London were evacuated.

And all flights into and out of the UK were set to be grounded.

The Foreign Office issued a hotline number - 020-7008-0000 - for people worried about relatives in the USA.

Notorious Saudi Arabian terrorist Osama bin Laden was believed to be behind the shattering attacks.

The terrorists hit right at the heart of America's financial district in a direct challenge to the most powerful democratic country on earth.

There was also an explosion at the Pentagon, the US defence HQ, at Washington after a plane crashed into it.

Part of the Pentagon, which had been packed with thousands of workers, had also collapsed.

The White House was evacuated by its terrified staff as the whole of the USA was put on red alert.

All flights have now been grounded in the United States.

Casualties were expected to run into thousands.

The onslaught of Palestinian terror rocked America - and sent shockwaves around the world.

It was initially reported that the Democratic Front for the Liberation of Palestine claimed it carried out the slaughter.

But the DFLP later denied that, saying it wouldn't kill innocent civilians.

A shaken President George Bush immediately vowed to hunt down the men of evil behind the sensational attacks.

He cut short a visit to Florida to return to Washington.

Prime Minister Tony Blair said the terrorist outrage was carried out by fanatics - and pledged to fight to "eradicate this evil from our world".

The first jet ploughed into the North Tower of the World Trade Centre - the tallest building in New York - at about 9am US time, 2pm UK time.

Some 18 minutes later millions of stunned TV viewers saw dramatic pictures of a second jet hurtling into the 85th storey of the South Tower.

There was a huge explosion and the aircraft vanished in an awesome mushroom cloud of flame.

Office workers screamed in terror and prayed for their lives.

One of the aircraft was a Boeing 767 which had taken off from Boston.

FBI agents were investigating reports that two United Airlines aircraft had been hijacked.

Aviation expert David Learmount told Sky News that "this is one of the most brilliantly militarily co-ordinated terrorist attacks the world has ever seen".

The horrifying double crash happened as 50,000 people went to work in the massive twin towers of the World Trade Centre - an enormous tourist attraction.

The scene was like something out of epic disaster film Towering Inferno as the building blazed like a torch.

Eyewitnesses said the first aircraft appeared to "bounce off" the massive 10.5 million sq ft structure and burst into a ball of flame.

Smoke poured out of the top of the 110-floor World Trade Centre - once the world's highest building - as the sensational pictures were broadcast all over the globe.

The nearby Wall Street money market hasn't started trading as a result while the FTSE 100 plunged through the floor.

The Queen sent her condolences to President Bush.

The World Trade Centre was also targeted by Palestinian terrorist bombers in 1993 but escaped serious damage.

Six people were killed and 1,000 injured in the atrocity eight years ago.

Thousands of aircraft regularly fly near the World Trade Centre to use JFK, La Guardia and Newark airports.

Over 200,000 people visit the World Trade Centre every day and 50,000 people work there.