Exports dropped by 7.9 percent to 1.5 billion Swiss francs ($1.5 billion), the Federation of the Swiss Watch Industry said.
"An unfavourable environment continues to hold back results in the sector," it said in a statement.
In 2015, watch exports recorded their first full-year decline since 2009, contracting by 3.3 percent with weakening Hong Kong demand already the main factor.
Hong Kong, which saw its 12th consecutive month of demand downturn in January, and the United States, where Swiss watch sales fell for the fifth straight month, are the two main markets for Switzerland's time piece exports.
Sales to Hong Kong dropped by a steep 33.1 percent last month, while sales to the US declined 13.7 percent.
Watch exports to mainland China eased by 1.9 percent in January.
Strength in Japan, up 35.8 percent, and across European markets was not enough to offset the downturn in the main markets, the federation said.