BEIJING, March 20 (Reuters) - Nickel and tin prices in Shanghai declined on Wednesday, as investors eyed more mining output from main producer Indonesia after it said will accelerate its approval process.

The most-traded May nickel contract on the Shanghai Futures Exchange (SHFE) declined 1.7% to a near two-week low at 136,910 yuan ($19,017.39) per metric ton by 0624 GMT.

The most-traded April tin contract fell 2.6% to 225,220 yuan per ton, after dropping as much as 3% - the biggest loss in three months - earlier in the session.

Prices of the metals in London fell on Tuesday after a senior Indonesian mining ministry official said the country had issued production quotas of 152.62 million tons of nickel ore and 44,481.63 tons of tin so far this year, and was working to accelerate the approval process.

The delayed issuance had sparked fears of supply tightness, supporting prices over the past few months.

"Signs of faster approval and better supply offset recently improved demand supported by better stainless steel production," analysts at Hongyuan Futures said in a note.

Nickel, a key metal for stainless steel and battery production, is plagued by a global supply glut. An executive at Vale said on Tuesday the market would swing to a deficit by 2028.

Three-month nickel on the London Metal Exchange rebounded 0.4% to $17,465 per ton, while LME tin was down 0.3% at $27,365 per ton.

Investors now focus on the U.S. Federal Reserve's monetary policy decision later in the day for further clues about the timing and quantum of interest rate cuts.

LME copper added 0.2% to $8,990 per ton, aluminium ticked up 0.1% at $2,272, zinc was up 0.3% at $2,271 a ton, and lead rose 0.2% to $2,094.

SHFE copper slid 0.8% to 72,690 yuan per ton, zinc shed 0.3% to 21,220 yuan, aluminium was little changed at 19,295 yuan, while lead climbed 0.3% to 16,280 yuan.

For the top stories in metals and other news, click or ($1 = 7.1992 Chinese yuan renminbi) (Reporting by Siyi Liu and Mei Mei Chu; Editing by Subhranshu Sahu and Varun H K)