(Feb 1): US stock index futures rose on Wednesday, in an upbeat start to February, buoyed by strong earnings from Apple, while investors awaited the Federal Reserve's decision on interest rates.

Apple's shares were up 3.01% at US$125 in heavy premarket trading after iPhones sales blew past expectations in the latest quarter.

The Fed is expected to keep interest rates unchanged in its first policy meeting after President Donald Trump took office as it seeks greater clarity on his economic policies. However, investors will parse the central bank's policy statement, expected at 2:00pm ET, for any changes following a string of strong economic data.

Investors are closely watching the quarterly earnings to support valuations after a post-election rally had driven Wall Street to record highs.

Earnings of S&P 500 companies are estimated to have risen 7.1% in the fourth quarter, driven by gains in financial companies, according to Thomson Reuters I/B/E/S.

While Apple is set to open at its highest level since July 2015, shares of other technology heavyweights also rose. Facebook, which is expected to report after markets close, was up 0.90%. Alphabet, Microsoft and Nvidia gained.

The S&P 500 and the Dow Jones Industrial Average marked losses on Tuesday amid concerns over the Trump administration's priorities. The Nasdaq Composite index managed to get a lift from biotech stocks.

A raft of data is expected to keep investors busy. A reading from the Institute of Supply Management will likely show that the US manufacturing activity index rose to 55 in January from 54.5 the previous month. The data is due at 10:00am ET.

US private employment rose to 165,000 last month compared to 153,000 in December, an ADP National Employment report at 8:15am is expected to show.

Among stocks, cloud-based communication platform Twilio rose 4% to US$30 after JMP Securities upgraded the stock to "outperform" from "market perform".

Mobileye was down 4.6% at US$41 after Morgan Stanley downgraded the stock to "equal weight" from "overweight".

Futures snapshot at 6:57am ET:

Dow e-minis were up 33 points, or 0.17%, with 15,876 contracts changing hands.

S&P 500 e-minis were up 4 points, or 0.18%, with 93,788 contracts traded.

Nasdaq 100 e-minis were up 24.75 points, or 0.48%, on volume of 18,797 contracts.