UPDATE 2-Pru gets HK listing OK, eyes Singapore-sources

* Listing on Singapore exchange under consideration-source

* HK exchange grants approval for listing -source (Adds Mason short position)

HONG KONG, April 22 (Reuters) - British insurer Prudential Plc (PRU.L) is considering a secondary listing on the Singapore Stock Exchange, as part of a wider plan to lure Asian investors to its massive $21 billion rights offer, sources said.

Prudential's Singapore listing news comes on top of its proposed Hong Kong listing plans. The Hong Kong exchange has granted approval to Pru's listing, one source with direct knowledge of the matter told Reuters on Thursday.

A spokesman for Prudential declined to comment.

Pru's Hong Kong listing is a key step in the process for its $35.5 billion purchase of American International Group Inc's (AIG.N) life insurance group, AIA.

Pru does not plan to raise capital through any of its Asian listings, but that would bring the company closer to its customers and shareholders.

Singapore's biggest sovereign fund GIC [GIC.UL] is among the large institutions that have committed to underwrite Pru's $21 billion rights offer, which would be partly used to fund the AIA acquisition. GIC currently owns a 0.5 percent stake in Pru.

Pru is betting big time on Asian growth by its planned acquisition of AIA, which is the biggest ever insurance deal.

Prudential has said it is seeking a primary listing in Hong Kong to attract Asian investors to the rights offer.

Separately, regulatory filings on Thursday showed hedge-fund manager Mason Capital Management had placed an almost 48 million pound bet on a fall in Pru's share price.

Mason disclosed a 0.38 percent short position, just days before Prudential is expected to disclose details of its capital raising in prospectuses for its listing and share issue.

The statement follows a similar announcement from hedge fund Lansdowne Partners on Wednesday, which showed a 0.32 percent short position. Lansdowne has since increased that position to 0.42 percent.

A source familiar with that situation said the holding was a "slight hedge" against a long position on UK banks.

Mason was not immediately available for comment. (Reporting by Denny Thomas and Kennix Chim; editing by Jacqueline Wong and Karen Foster)