In spite of the sharp increases, the latest global office survey conducted by international chartered surveyors CBRE Richard Ellis still puts SA rent at the bottom range of more than 200 cities.

More alarming is that local rents, growing at about 20%/year, are not rising as fast as in many cities, as the SA office market is still recovering after more than 30 years of decline since the 1970s. This means that local rents can be expected to rise even further. London has the world's highest rents at R1 569/m2/ month compared with Cape Town's R126/m2. Jakarta has the lowest prime office rents at R101/m2.

"There's a shortage of prime office space and there's a tenants' bidding war going on," says Pace brokers CEO David Green. "It's not impossible that rents will break through R200/m2 in the near future. But I don't know where it will end."

CBRE Richard Ellis's Dave Alcock says building costs will be the main driver of office rents as SA competes with the world for skills and materials.

Higher rentals will result in companies squeezing more staff into less space. Some tenants may also try to pass the increased costs on to their customers.