BOA has leased four floors, totalling 115,000 square feet, to become the joint largest single tenant in the Swire development.

It is thought a shake-p will take place in Bank of America Tower and at the offices of Security Pacific Asian Bank at No 9 Queen's Road Central.

The two companies have merged and will officially become Bank of America Asia at the beginning of next month.

The deal also means that Devon House is now fully leased - just three months after gaining its occupation permit.

A spokesman said back office operations would be moved to Quarry Bay, with customer service related facilities staying in Central.

Four floors have been sold in the tower to an investor - whose identity is not known - and two podium floors retained.

It is also thought Security Pacific is negotiating to terminate the leasing of about 60,000 sq ft of space at its headquarters.

The BOA spokesman said: ''The move is basically to do with costs. The rentals in Central are rising and there is cheaper accommodation elsewhere.

''It is really to protect the long-term viability of our operations here.

''Exactly who will be moving is still being worked out.'' The keys to the new base will be handed over at the beginning of next month.

BOA will then design and fit the new offices before employees are moved in on a staggered basis towards the end of the year.

Rents at Devon House are thought to average between $25 and $30 per sq ft net per month.

In Central - where rents have shot up sharply in recent months - some landlords are now demanding up to $60 for whole floors and up to eight dollars more for smaller spaces.

Big firms such as Hewlett Packard, AT & T, Standard Chartered Bank and American Express have either left Central completely or moved back-room operations away recently.

One analyst said: ''They are not doing it because they are getting annoyed with the high rent levels in Central.

''In fact, rents have still got some way to go, when you take account of inflation, before they hit the peaks of 1988.

''Firms are taking advantage of the top quality accommodation which is now being built in less traditional areas like Quarry Bay.

''It makes sense because it is quite simply cheaper.'' Stewart Jones, of Vigers, said: ''Since quality Grade A developments started to appear in less established business districts, large space users have been seizing on the opportunity to achieve significant cost savings.

''Most quality developments in North Point and Quarry Bay have been received well in the marketplace.''