The S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) has plummeted another 103 points, or 2.1% today, taking the benchmark index below 4,900 points to its lowest level in two-and-a-half-years.

Following a rather disappointing 2015 calendar year, investors were hoping for bigger and better things in 2016 with some experts suggesting a return to 6,000 points by the year’s end. That currently seems like a long shot, with the ASX suffering through what has been one of the worst starts to a new year in history, driven by plunging oil prices and disappointing economic data from China.

Source: Google Finance

Source: Google Finance

The pain has once again been widespread today, with the miners wearing the brunt of the damage. Rio Tinto Limited (ASX: RIO) and Fortescue Metals Group Limited (ASX: FMG) shares have fallen 4.2% and 5.5% respectively, while BHP Billiton Limited’s (ASX: BHP) share price has plunged 4.4% to $15.63 after hitting a fresh 10-year low of $15.57.

The major banks have also been hit hard. Commonwealth Bank of Australia (ASX: CBA) and Westpac Banking Corp (ASX: WBC) both fell 1.8%, while Australia and New Zealand Banking Group (ASX: ANZ) and National Australia Bank Ltd. (ASX: NAB) fell 1.7% and 1.6%, respectively.

Some of the other heavy fallers included Telstra Corporation Ltd (ASX: TLS), down 0.9%, Macquarie Group Ltd (ASX: MQG), down 3.2%, and iSelect Ltd (ASX: ISU), down a merciless 31.8%.

As tempting as it might be to sell into the panic on these days, investors should avoid that temptation and ensure they remain calm and composed. Those investors who control their emotions and hang on for the greener pastures will likely be the ones rewarded in the long run.

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Motley Fool contributor Ryan Newman has no position in any stocks mentioned. Unless otherwise noted, the author does not have a position in any stocks mentioned by the author in the comments below. You can follow Ryan on Twitter @ASXvalueinvest.

The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.