On a brutal day for the major averages, CNBC's Jim Cramer decided to open the phone lines to investors worried about the state of the stock market.

The "Mad Money" host's overarching message? "The time to start buying may be upon us," because what started as selling has now grown into what seems to be a full-blown panic, he said.

"A vicious correction is, indeed, a terrible thing to waste," he told viewers. "If you have some spare cash or if you're thinking about putting some long-term money away at the end of the year, maybe you pull some of it forward. That's what I did today for my kids' index fund."

The reason Cramer felt a bit better about buying was due to a trend he noticed in the market's trading volume. Investors were selling at a 10 to 1 rate, meaning the volume was heavily skewed to the downside, a sign that things could be getting oversold.

"On a day when volume was 10 to 1 on the downside, I am OK'ing small buys of some of the great stocks that we have followed and talk about, the big generational changers — the cloud kings, the FANGers. Maybe just pick one or two," he said, referencing his widely known acronym for the stocks of Facebook, Amazon, Netflix and Google, now Alphabet.

Still, investors have to be more selective now than they were before the sell-off, the "Mad Money" host said.

"We have to understand that companies will not be as bullish as they were because of the tariffs, because of higher interest rates, because of the consequences of full employment, because of margin squeezes and a host of other things," he explained.

"So, as I have been saying, we will have to be a lot more selective in any industry, and while I think it's OK to start buying small, remember: your first buy may not be your only buy. And buy quality, please, and nothing less," he continued.

And whatever you do, don't feed into the panic and sell without reviewing the fundamentals, Cramer said.

"The time to do the big selling … may have come and gone," he told investors. "That doesn't mean you shouldn't take profits if you've got some, but the idea to continue to sell after what happened today? That may be ill-founded."