Last minute rehearsals for this week's wedding of Prince William and Kate Middleton got under way before dawn in central London on Wednesday with the royal couple expected to put the final touches to their preparations.

Roads around Buckingham Palace and along the route the couple will take from Westminster Abbey after Friday's service were closed as about 1,000 members of the armed forces took part in a full-scale practice for the couple's big day.

Carriages that will carry members of the wedding party also took part alongside mounted cavalry, with a full dress-rehearsal involving the clergy and broadcasters scheduled for Thursday.

The abbey itself has already been closed off to the public, and William and Middleton will be there for some final rehearsals on Wednesday, although royal officials declined to give details.

"As with anybody's wedding, you can imagine rehearsals happening up until the eve of the wedding," a spokesman for William said.

Across the capital, bunting is going up and flags are beginning to be hoisted, while a small army of media from around the world has descended on makeshift studios set up outside Buckingham Palace and along the route.

The ceremony is predicted to attract a global TV audience of some two billion people.

"We have been coming over in waves, we have a cast of thousands," said NBC Washington news anchor, Wendy Rieger.

"I called back to work yesterday, and said the only Americans I can find here right now are people with cameras on their shoulders, you know. The media is bumping all over each other," she told Reuters TV outside Westminster Abbey.

Some royal fans have already begun camping outside the abbey to secure the best spots to watch Friday's events, and hundreds of thousands of people are expected to start arriving in London in the next days.

More than a million visitors

VisitBritain, the national tourism agency, is predicting an extra 600,000 tourists in the capital on the day, meaning there would be a total of some 1.1 million visitors with 40 percent of those coming from abroad.

"That could bring anything up to 50 million pounds," a spokesman said.

The number of in-bound flights to Britain for the weekend had risen by 244 percent while online travel booking company Expedia said hotel bookings had surged 266 percent when the wedding date was announced, the spokesman added.

London and Partners, the agency which promotes the city, said it expected there would be 600,000 people actually lining the streets, the same number as came to watch the 1981 wedding of Prince Charles to Princess Diana.

Despite the interest, those planning last minute trips could still find somewhere to stay.

"From what we're being told by contacts in the industry there are still rooms available," a spokeswoman said.

However, anyone coming to London to watch the procession or camping out could be in for a cold and wet experience, with weather forecasters predicting showers and a brisk wind.

On Tuesday, police appealed to the public to help them spot any potential troublemakers, while promising that they would not tolerate any attempt to disrupt the event.

Some 5,000 police officers will be on duty to deal with potential threats ranging from international Islamist militants to anarchists and stalkers.

Meanwhile the one-and-a-half mile processional route has undergone a deep clean to get it looking spic and span.

A team of 130 street cleaners including 80 sweepers along with 30 vehicles are being lined up to deal with the 140 tonnes of waste expected to be left by those watching on Friday.