HK shares retreat 3.7 pct as HSBC, China Mobile drop

* HSBC sinks in global bank stocks sell-off

* China Mobile drops after first quarter earnings

* Gold miners buck trend on safe haven appeal

By Parvathy Ullatil

(Updates to midday)

HONG KONG, April 21 (Reuters) - Hong Kong shares fell 3.72 percent by midday Tuesday in a broad-based sell-off while shares in HSBC slumped after Bank of America (BAC.N) reignited concern over credit quality deterioration at global banks.

The other index heavyweight, China Mobile (0941.HK) slid 5.52 percent to HK$70.20 after its first-quarter earnings growth slowed to 5 percent, prompting analysts to lower their earnings forecasts on the world's largest wireless service provider.

JP Morgan cut its 2009 profit estimate by 4.8 percent and that for 2010 by 9 percent to factor in lower usage and revenue-per-user assumptions. Intensifying competition and its rural market thrust is also seen clouding China Mobile's outlook further.

The benchmark Hang Seng Index .HSI ended the morning session down 585.44 points at 15,165.47.

Shares worth HK$33.2 billion had changed hands compared with midday Monday's HK$33.3 billion.

The still-strong turnover seemed to suggest there was further upside to the market despite Tuesday's pullback, said analysts.

"Institutional flows have been very strong in past few weeks and if you just look at Hong Kong and China, corporate earnings and economic data seem to be improving," said Steven Leung, director with UOB Kay Hian.

"So even if there is big sell-off in the near term, the market may bounce right back because there are enough institutional buyers waiting to enter this market at a more attractive level" he said.

Europe's top bank HSBC (0005.HK) retreated 5.82 percent to HK$51.75, while Standard Chartered (2888.HK) pulled back 6.2 percent after Bank of America raised doubts about the sustainability of the recent earnings bonanza from U.S. banks.

Shares in the U.S. lender plunged 24 percent despite the bank reporting a rise in profit after its chief executive warned the bad credit environment was getting worse.

Local utility stocks bucked the downtrend to edge up as investors turned to defensive plays inlcuding Hongkong Electric (0006.HK), up 1.1 percent, and CLP Holdings (0002.HK) which was up 0.67 percent.