Singapore: Oil prices were down in Asia Wednesday as investors awaited the result of a US central bank meeting and a closely-watched report on crude inventories in the world's biggest economy.

Worries over the Chinese economy after a rout in the country's stock market and a global crude oversupply were also keeping buyers at bay, analysts said.

US benchmark West Texas Intermediate for September delivery fell 14 cents to $47.84 and Brent crude for September gave up 13 cents to $53.17 a barrel in afternoon trade.

The policy-setting Federal Open Market Committee (FOMC) of the US central bank will issue a statement at the end of a two-day meeting Wednesday, and investors are hoping for clearer signs on the timing of a US interest rate increase.

A rate rise will boost the greenback, making dollar-priced oil more expensive to holders of weaker currencies, hurting demand and helping push crude prices lower.

Investors will ‘pay close attention to the text of the FOMC statement for any confirmation/insights for the timeline of the first rate hike’, Singapore's United Overseas Bank said in a note.

‘I feel that (Federal Reserve chief Janet) Yellen will continue to lay the ground for an imminent interest rate increase,’ said Bernard Aw, market strategist at IG Markets Singapore.

‘We may see a modestly upbeat spin on economic prospects in the policy statement, which would underpin expectations of a rate hike this year.’

The market is also awaiting data later Wednesday of last week's US crude inventories as American oil drillers ramp up production despite the supply glut that has depressed prices.

A plunge in Chinese shares this week has stoked fears that demand from the world's second biggest economy will be affected.

Chinese stocks ended the morning session 0.21 per cent lower Wednesday, erasing earlier gains and extending a more than 11 per cent plunge in the previous three sessions.