Damian McBride appeared to suggest that the stock market dip could lead to civil disorder or other situations where it would be unreasonable for someone to leave the house.
“Advice on the looming crash, No.1: get hard cash in a safe place now; don't assume banks & cashpoints will be open, or bank cards will work,” he tweeted.
“Crash advice No.2: do you have enough bottled water, tinned goods & other essentials at home to live a month indoors? If not, get shopping.
“Crash advice No.3: agree a rally point with your loved ones in case transport and communication gets cut off; somewhere you can all head to.”
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Mr McBride credited his former boss Gordon Brown with preventing a cataclysm by nationalising the banking system during the 2008 crash.
“We were close enough in 2008 (if the bank bailout hadn't worked),” he said. “and what's coming is on 20 times that scale”.
Financial markets are unstable and periodically suffer crises which can have devastating consequences for the wider economy.
The Shanghai Composite Index, China’s most important stock market index, was down 8.45 per cent, erasing a year’s gains in a day’s trading.
The FTSE100 fell 4.5 per cent, hoping £60bn off the price of UK shares, and the Dow Jones in the US fell by over a thousand points in its first minute of trading.
Some analysts have suggested that the stock market slide could be the start of a new global financial crisis.
Mr McBride’s suggestions about stocking up on canned goods, setting rally points and stocking up on bottled water were ridiculed by some users on Twitter as over the top, however.
Mr McBride was special adviser to Gordon Brown and head of communications at the Treasury for a period during the last Labour government.