By Ryan Dilley BBC News Online correspondent in New York

The rescue effort at the site of the wrecked World Trade Center continues, but already a vigorous debate has begun about what, if anything, should be built there once the mammoth task of clearing the rubble is completed.

In a city of skyscrapers, the World Trade Center towers stood above all others. Touring their smouldering remains, New York State's shocked governor George Pataki said he was disorientated by the loss of a familiar reference point in the city's skyline.

The skeletal remains of Hiroshima's A-bomb Dome

In other cities scarred by terrorism and war, famous buildings have been rebuilt brick by brick - or, in the case of the twisted ruins of Hiroshima's Chamber of Commerce, left as a reminder of lost lives.

In the UK, blitz-damaged buildings such as the Victoria and Albert Museum were restored after the war, but allowed to retain some of the scars and pockmarks left by the Luftwaffe bombs.

Larry Silverstein, who took out a 99-year lease on the WTC site in July, says some structure should go up on the 16 devastated acres.

Monument to the dead

Already there have been calls for the two 110-story towers to be rebuilt, despite fears that the ground around the site can no longer support the foundations of such massive structures.

Empty chairs for each of Oklahoma's 168 victims

One host of a popular American TV breakfast show agreed that exact replicas should be constructed, but that no-one should be allowed to occupy the offices. Instead this new WTC would stand as a monument to those who died in its horrific collapse.

Another idea is to create a monument at ground level. At the site of the Oklahoma bombing, the devastated Alfred P Murrah Federal Building has been replaced with a memorial park.

Rows of 168 metal chairs fill the space, one for each of the 1995 bomb's victims.

I don't think New Yorkers would let such a large parcel of valuable land remain unused

Brendon Heneghan

Brendon Heneghan fled his 79th-floor office in the WTC's Tower Two, minutes before the second hijacked airliner struck that level of the building. He says he expects only a portion of the site to remain as a memorial to the lost, who include 19 of his own colleagues.

"It's not a matter of whether they will build, but how high. New Yorkers are very resourceful and matter-of-fact and I don't think they'd let such a large parcel of valuable land remain unused."

Too many memories

Turning the whole of it into a park would effectively ruin the business atmosphere of the area.

The attacks left a gaping hole in the skyline

Mr Heneghan says building a "skeleton" of the WTC would be wildly expensive.

"I'd build something as tall as the tallest remaining building in the vicinity. The World Financial Center is about 55 floors high."

The banker says creating an exact replica would bring back too many bad memories.

"People wouldn't want to work in it or in its shadow. It should be a building you wouldn't feel vulnerable working in."

Mr Heneghan echoes the fears of many that a 110-story structure would be too upsetting a sight for those affected by the 11 September attack and more worryingly offer the terrorists another tempting target.

Oklahoma City built the memorial on the bombsite

"If the World Trade Center wasn't so tall it might not have been seen a symbolic target for last week's terrorists or those who planted the bomb."

The grieving firefighters of Manhattan's Engine Company 23, whose numbers were decimated in the WTC collapse, say risk or not the towers should go back up.

Lieutenant Vernon Davis does not hesitate for a second before saying: "They should build it back exactly the same, no, bigger. Bigger in defiance of the perpetrators of this heinous crime."