* Approved $2.3 bln out of the $7 bln investment on Monday
* Samsung No. 1 in NAND flash revenue in Q2 with 38.3 pct -IHS
* Firm announced $18.6 bln investment in South Korea in July (Adds background, Samsung NAND share)
SEOUL, Aug 28 (Reuters) - Samsung Electronics Co Ltd expects to invest $7 billion over the next three years to expand its NAND memory chip production in China's northwestern city of Xi'an, the South Korean tech giant said on Monday.
In a regulatory filing Samsung said it approved $2.3 billion of the expected investment of $7 billion on Monday.
In early July, when Samsung announced an investment of $18.6 billion in South Korea, it said it would add a production line at its NAND plant in Xi'an, but did not set an investment amount.
A Samsung Electronics spokesman declined to comment on the amount of capacity to be added by the approved or planned investment.
The firm accounted for 38.3 percent of global NAND flash memory chip revenue in April-June, the latest data from researcher IHS showed.
China is trying to develop its own memory chip producers but it is likely to be several years before they can compete with existing makers, analysts said.
Samsung Electronics said a memory chip boom that propelled it to record profit in the second quarter was likely to continue in the July-to-September quarter. (Reporting by Joyce Lee; Editing by Kim Coghill and Clarence Fernandez)