The US Federal Reserve has cut interest rates to 3.5% after huge declines in shares across Asia and Europe on Monday.
Here, BBC website readers describe how the stock market jitters have affected them.
SARAH POCOCK, LONDON
I fear that if there's a downturn in the economy it'll affect young professionals like me who are already struggling with debts.
I'm 28 and was in the first year of students to receive no grant, whose parents had to pay the full tuition fees.
I entered employment with a massive loan - it'll take till I'm 35 to pay off.
After saving for seven years I've just bought a small two-bedroom house with my partner in a poorer part of London. Now I'm worried that I may be hit by negative equity if house prices start to tumble.
Banks have been irresponsible in recent years encouraging people to borrow money so they earn money on high interest repayments.
A bit like the '80s this has fed into a culture of 'spend, spend, spend' - which I think is at the root of the problem.
Maybe the latest events will encourage people to be more cautious. But maybe not. Glossy magazines are still selling us a lifestyle most people can't afford.
BALWANT MUNGLANI, NORTHWOOD, LONDON
I am 71 and my life savings are threatened with the collapse of the stock market. I have cut my losses on some of my investments by cashing them in.
The 0.75% cut by the Federal Bank of the USA is a clear acceptance that the world economic order is shaky. This is a gamble that will not work unless fundamentals are corrected.
Banks have been lending irresponsibly for some time - lending mortgages at five or six times people's salaries seems ridiculous.
This lending has also fed into the hike in house prices which surely can't be good for the economy.
In the UK we've been hit by a double whammy of the credit crunch in the US - which in my mind just means irresponsible lending - combined with irresponsible lending from our own banks.
All this has not been helped by the US and the UK governments spending unwisely - including on expensive foreign wars.
I think we are in for a very long haul - it could take five or six years to get through this problem, no thanks to our friends in America.
PAUL ROBINSON, BILLERICAY
Pretty much all my savings are invested in the stock market, although they are all in blue-chip companies.
Nevertheless, some of my portfolio has taken a really bad hit - it's probably shrunk by about 30%.
I have to say, I am worried. The blame is clearly with the banks and their irresponsible lending and now everyone is paying the price for it.
I think there has to be more regulation on the industry.
I also think the system of reporting quarterly accounts can be improved so that there is greater transparency between reports about how well or badly a company is doing, so that the market remains more stable.
I started investing in the stock market about three years ago - I used to work in the city and this is clearly the most worrying time I've had so far.
All I can really do is sit tight - I can't afford to panic sell. I wish I had kept some money aside for when a downturn like this came along - I think it's a good time to buy stock in terms of the value you could get for it.
LORRAINE KIRBY, ST ALBANS
I'm a regular small-scale investor in the stock market and I expect that over the long term the prices will recover.
I've been investing in the stock market for about 20 years, in a mix of tracker funds and stock that I have chosen myself.
You just have to wait until the market settles down
Some of the stocks have dropped in value by nearly 30% in the past few days.
But I'm not worried by the current situation.
I always take the long term view with my investments - of up to 15 years in the case of some of my stock.
The one thing I'll make sure not to do is turn a paper loss into a real loss. I would be mad to try and sell up now.
I'm not sure if there is anything that can really be done to change the market.
I work in commodities and know full well that when there is a bad vibe in the air, then that can lead to people acting on it - you just have to wait until the market settles down.