After several years of record growth, exports last year fell by 3.3 percent to 21.5 billion francs ($21.2 billion), the Federation of the Swiss Watch Industry (FHS) said.
In 2014, by contrast, Swiss watchmakers had clocked a historic 22.2 billion francs in exports - up 1.9 percent over the previous year.
Last year's drop was the first since the sector was slammed with a sharp slowdown in 2009 in the aftermath of the global financial crisis.
The 2015 slump was closely linked to a steep 9.1-percent fall in demand in Asia, the main market for Swiss watches, which absorbed exactly half of all the exports last year.
In particular, "development of the Hong Kong market weighed heavily in the overall balance," FHS, pointing out that the key market for luxury timepieces had contracted 22.9 percent in 2015.
The federation explained that the local Hong Kong market had undergone "a major readjustment linked in particular to exchange rates and consumer trends."
The decline in watch exports by nearly a quarter in the semi-autonomous region, which is still feeling the impact of the pro-democracy Umbrella protests which brought much of Hong Kong to a standstill in 2014, had exerted "a strong negative effect on the result worldwide," FHS said.
Exports to mainland China were also down 4.7 percent last year, although they were seen improving towards the end of the year, bouncing up 5.5 percent in December, FHS said.
China anti-corruption drive
Exports to China have yo-yoed wildly in recent years, first raking in several years of double-digit growth before taking a hard hit following efforts to crack down on corruption in that country by banning extravagant gifts like expensive watches to public officials.
Overall, FHS stressed that "the general context did few favours for the branch", pointing to the changes in Hong Kong as well as "the economic slowdown and political decisions in China, tensions in the Middle East, the low level of the ruble and terrorism" among other factors.
The overvaluation of the Swiss franc since the Swiss central bank last January suddenly decided to stop artificially trying to hold down its value against the euro had also dealt a blow to exports from Switzerland, it said.
"This situation will continue to influence results for the Swiss watch industry in the first part of 2016, which moreover will suffer from a generally unfavourable base effect," FHS warned.
As a consequence, Swiss watch exports "are likely at best to achieve the same value this year as in 2015."