UPDATE 1-Apple expands iPad sales to 9 more countries

* To go on sale in new markets on Friday

* Markets include Mexico, Hong Kong, Singapore

* Plans to add 'many more countries' later this year

BOSTON, July 19 (Reuters) - Apple Inc (AAPL.O) plans to start selling the iPad tablet PC, its latest hit product, in nine new international markets on Friday, making the device available in a total of 19 countries.

The new markets are Austria, Belgium, Hong Kong, Ireland, Luxembourg, Mexico, Netherlands, New Zealand and Singapore. Apple had previously said it would add those countries some time during July.

Apple introduced the device on April 3 in the United States, then on May 28 expanded sales to nine other countries, including Canada, Japan and Europe's biggest countries.

The maker of the iPhone and Mac computers said it expected to add "many more countries" before the end of this year, although it did not provide further details.

Wall Street estimates that Apple sold some 3.3 million iPads during its most recent quarter, which ended June 30. The company is scheduled to release quarterly financial results on Tuesday. (Reporting by Jim Finkle; Editing by Lisa Von Ahn)