Cortina Holdings Ltd, which has outlets in Southeast Asia, Taiwan and Hong Kong, said it discovered the theft last Friday.

"The theft involves timepieces at a net cost of about 7.9 million Singapore dollars ($5.5 million)," Cortina said in a statement late on Monday to the Singapore Exchange.

The theft occurred at Cortina's outlet in the central Raffles City shopping mall after the close of business on Christmas Day and before the store opened on Friday, it said, adding that the incident would hit the company financially.

Police said they were investigating the theft, one of the largest in recent memory in the city-state which prides itself on tight security and a low crime rate.

Yesterday the shop was open for business with sales staff standing behind counters displaying the store's high-end watch brands.

The shop, located prominently on the ground floor in front of escalators, appeared not to be damaged but staff declined to be interviewed.

Cortina's public relations officer, Susan Yang, also would not answer any questions.

"Sorry we can't comment (on) anything at the moment because it's under investigation," she said from the head office.

Nur Zaliza Ahmad, who works at a shoe store across from the Cortina outlet, said she went to work at about noon last Friday and saw a sign saying the watch shop was closed for a "stock-take".

Later, at about 4:00 pm, she saw a uniformed policeman inside while staff were counting watches.

Cortina carries luxury brands including Audemars Piguet, Patek Philippe and Cartier, which can retail for thousands or even tens of thousands of dollars each.

The company said it had tightened security at all its retail outlets after the incident.

"The board is taking steps to conduct a comprehensive review of the group's security procedures and recommend measures for improvement," the statement to the Singapore Exchange said.

Earlier this year Cortina Holdings reported a 200 percent year-on-year increase in net profit to 9.5 million Singapore dollars for the financial year ending March 31. Group sales were up 20.5 percent from the previous year, to 238.6 million dollars, the firm said.

The theft will have "an adverse impact" on financial results for the year ending next March, Cortina said in its Monday statement to the Exchange.

The company was founded in 1972.