By Neil MacLucas

ZURICH--Swiss watch exports increased 6.9% on the year in July, driven by ongoing robust demand from Asia, data released Thursday by Switzerland's customs office showed.

The value of watch exports reached 1.97 billion Swiss francs ($2 billion) in July, up 6.9% in real terms from the same month a year earlier. In nominal terms, the gain was 15.4%, the office said.

Swatch Group AG (UHR.VX), Compagnie Financiere Richemont SA (CFR.VX) and privately held Rolex are the main producers in the Swiss watch market.

Shares in Swatch closed Tuesday at CHF403.70, up 16% in the year to date. Those of Richemont closed at CHF60.65, for a gain of 30% in the same period.

Write to Neil MacLucas at neil.maclucas@dowjones.com