Sources in the former colony say the contractor is hoping to finalise the sale before the end of July.
A deal would make commercial sense for Emcor Drake & Scull as one of its strategic aims is to expand YDS Engineering, its Chinese facilities manager. Citex Asia would come with a contract to provide FM and project management services for one of Hong Kong's biggest players, HSBC, until 2004.
Emcor Group has a track record of winning work in Hong Kong, including a cargo terminal at the £1bn Chek Lap Kok airport and a metro system.
It had considered a tie-up with Citex Asia over FM work at Chek Lap Kok, according to local sources.
The upcoming sale of Citex Asia, which is expected to turn over £17m in the year to 30 April, came to light after Building saw a copy of a memorandum of sale written by KPMG and circulated to possible bidders.
The memo pointed to changes in Citex Asia's income, including the loss of an FM deal with telecoms provider PCCW, which would lead to a cut of one-third in the company's turnover.
KPMG recommended that in view of this, Citex should dispose of the subsidiary or seek to merge it with a local partner.
Another factor in the decision to sell was the weakening of the Hong Kong market. According to figures released last year, construction work in the private sector has dropped by about 30% compared with 1997, the year the colony was handed back to China.
Other potential bidders for the arm could include rivals working in the region, such as Jardine Property Management, Trammell Crow Savills, Johnson Controls and Jones Lang LaSalle.
Citex chief executive Oliver Jones refused to comment on the potential deal. He said: "I would never comment on commercial matters such as these."
Emcor Group has a turnover of £2.1bn and employs 23,000 staff worldwide.
The firm is understood to have been selected by client Chelsfield, which has also picked a shortlist of major contractors to oversee the project.
Sir Robert McAlpine, Laing, Bovis Lend Lease and Multiplex are all interested in taking on the scheme, which is expected to create 1800 full- and part-time jobs during construction.