Frankfurt's office rents are soaring, fast outpacing the vertical growth of the city's skyline. Floors in Frankfurt's elegant, pencil-shaped Messe Turm are understood to have been let last month for a record DM100 (Euros 51) per sq m.

Estate agents say rents, which have risen more than 30 per cent in two years, will climb even higher in the coming months as demand outstrips a strictly limited supply.

"We have not seen the top of the market yet," says Richard Tucker of CB Richard Ellis, the property agents. "About DM90 to DM100 (per sq m) is normal now for state-of-the-art offices." Driving the rental boom is Frankfurt's rapid expansion as continental Europe's leading financial centre.

Banks and financial services groups, telecommunications companies and business consultancies are flocking to the city, home to the European Central Bank and Europe's premier market for high-growth, high-risk shares - the Neuer Markt.

The three sectors account for more than 70 per cent of demand, say analysts, with banks and financial services companies generating almost 40 per cent of lettings. Mr Tucker expects rents in Germany's most expensive property market to peak in the second half of next year as more space becomes available. However, Yves Orsenigo of Muller International, the property agents, says it could be another two years before there is enough space to satisfy demand.

Meanwhile, desperate companies are scouring the most sought-after districts the Westend and the Banking Viertel. The problem, says Muller International, is that tenants are increasingly demanding.

"They want state-of-the-art cabling space and air-conditioning is now a standard requirement in high-grade office premises," it says in its latest research. Estate agents say the search will be difficult. The office vacancy rate is at its lowest level for years, at about 4 per cent - just 390,000 sq m of the total market of about 9.5m sq m - according to CB's Richard Ellis. And much of the space available is in properties that were built before 1985.

Many companies are being forced to look out of town, to neighbouring but "less desirable" Eschborn or Niederrad, where rents are about DM28 per sq m, say agents. Others are looking to rent premises that are still under construction or at the planning stage, says Muller.

Agents say companies are also increasingly asking for different kinds of space. Combi-offices, which link single rooms with a common communication zone, are in demand and so are open-plan areas, especially for banks and financial services companies. Open floors now account for about 9 per cent of demand, says Muller. CB's Richard Ellis estimates that 60 per cent of all lettings over the past six months have been for properties of more than 5,000 sq m.

Banks want open-plan floor spaces for trading rooms and back-office operations. But these are difficult to find in the high-rise buildings and older properties that dominate the prime letting areas. Some of the latest city centre projects - the Main Tower and the Frankfurter-Welle, for example - offer trading floors. Three of the big commercial banks - Deutsche, Dresdner and Commerzbank - are building their own trading centres.

Traditional high-rise structures, however, will continue to predominate in the city's core business districts and offer the best hope of easing the supply squeeze. Badly damaged during the war, Frankfurt am Main made little effort to restore its pre-war architecture. Instead, the city, fond of referring to itself as "Mainhattan", built skyscrapers.

It already has Europe's tallest building, the Commerzbank tower, which was designed by Norman Foster, and Deutsche Bank's twin towers, an icon of Finanzplatz Deutschland. But city planners have given the go-ahead for about 20 more skyscrapers under the "high-rise blocks for Frankfurt" plan, an urban planning study that was approved in 1998.

Not all of them will be built, say agents, because the grand designs of many developers will founder on the city's regulations. Frankfurt likes its towers but requires that they provide more space and light per staff member than many other building regimes. Estate agents say Frankfurt's high-rise growth should increase the amount of office space by up to 50 per cent over the next few years.

First up will be Dresdner Bank's Galileo, two glass towers that will provide 52,000 sq m of additional space in 2002. The bank says it is building the tower for its own use but agents say plans may change if rents continue to increase. Deutsche Bank's "Max", providing about 65,000 sq m, should be completed by 2004.

At about the same time, the DM7.5 billion Europa Viertel, one of the biggest construction sites in Europe, will begin to complete office buildings and apartments, along with an entertainment complex and hotels. By 2006, this former rail freight yard, close to Frankfurt's exhibition centre, will also feature the DM380 million Millennium Tower, Europe's tallest building. It has already caught the eye of Donald Trump, the flamboyant American businessman who has been the biggest operator on the New York property scene for more than two decades.

He has expressed an interest in joining the project as a developer and this month held talks with Petra Roth, Frankfurt's mayor. A Trump Tower from the "anything you can do I can do bigger" American businessman could give another boost to "Mainhattan's" high-rise ambitions.