CEOs are warning of a recession. Here's what they're saying, and their advice on how to prepare.

According to the Tesla and SpaceX CEO, the US has already entered a recession, and things are about to get worse.

"What tends to happen is if you have a boom that goes on too long, you get a misallocation of capital," he said May 16 at the Miami tech conference All-In. "It starts raining money on fools, basically."

Musk said that a hallmark of the type of economic picture he's describing is when people are "doing things that are silly and not useful to their fellow human beings" — typically, those "bullshit companies" will go bankrupt, he said.

Musk's advice for how to deal with a recession? Make a useful product and make sure your company makes sense.

"Make sure you're not running things too close to the edge from a capital standpoint," he said, adding that companies need capital reserves to make it through "irrational times."

A downturn is going to be "hard to avoid," according to Wells Fargo CEO Charles Scharf.

"You've got the Fed saying the economy is running too hot, that we need to slow economic growth. Rates are going to rise, and it's going to change the dynamic of the health of the consumer and business over a period of time," Scharf said on May 17 during the Wall Street Journal's Future of Everything Festival.

That being said, Scharf believes that many businesses are heading into a downturn with an advantage: resiliency.

"The fact that everyone is so strong going into this should hopefully provide a cushion such that whatever recession there is, if there is one, is short and not all that deep," he said.

Best Buy CEO Corie Barry is expecting an economic slowdown, but not a full recession, she said during the company's first-quarter earnings call.

"It's fair to say we're factoring in for softer demand, but we're not planning for a full recession — our guidance does not assume a full recession at this point," Barry said.

But Barry noted that consumer electronics is a "very stable industry," which she said has been proven by the pandemic.

"The last two years have clearly underscored the importance of tech in people's lives, so I think that's important to have that as backdrop," she said. "And the fact that we were already planning for our industry to decline this year, and we're adjusting based on results."

The Goldman Sachs CEO estimates there's a 30% chance of recession over the next 12 to 24 months, he told CNBC's Andrew Ross Sorkin on May 18.

"There's a reasonable chance at some point that we have a recession or we have very, very slow, sluggish growth," he said.

His advice for his fellow execs is to start considering your risk appetite — and to start preparing for a slowdown.

"That doesn't mean that that's definitely going to happen, but certainly, I think that if you're running a significant enterprise, you have to be looking through a lens with a little bit more caution right now than you might have been when we were sitting here a year ago," he said.

The US economy is currently at "very, very high risk" of recession, Goldman Sachs Senior Chairman Lloyd Blankfein said on CBS's "Face the Nation" on May 15.

However, Blankfein still took an optimistic bent, praising the Fed's response and the "powerful tools" at its disposal to help avoid recession.

To that end, he advised preparedness but not panic.

"If I were running a big company, I would be very prepared for it. If I was a consumer, I'd be prepared for it," he said. "But it's not baked in the cake."

Anthony Capuano, CEO of the hotel chain Marriott International, believes a downturn is imminent.

"The chorus of voices saying we're careening towards a recession are getting louder by the minute," he told The Wall Street Journal at the World Economic Forum last month.

He added: "Time will tell, but it certainly seems we're headed in that direction."

YouTube CEO Susan Wojcicki has lived through a few recessions during her time at Google, so she has a plan for weathering a downturn: take the long-term view.

Speaking May 24 at the World Economic Forum, Wojcicki described her economic outlook from the helm of the world's largest video-sharing platform. While a slowdown is "challenging, there's no doubt about it," Wojcicki says YouTube has always come out stronger in the end.

"We actually get better at what we do," she said. "When your numbers are going up all the time, it's really easy to be like, 'OK, things are good.' When they're going down or they're not going as fast as you expect, suddenly you are really digging into the details."

And right now, YouTube has no plans to slow down.

"There may be areas where we may decide to delay starting a certain project, but in general, we're still saying, 'This is an important business, we're going to grow, we're going to continue to invest here," she said.

Palantir CEO Alex Karp says executives are generally feeling pessimistic right now, and that it's part of a cycle.

"There is a cycle of mood," Karp told The Wall Street Journal at the World Economic Forum. "You walk around and everyone thinks it's going to be bad, so it's going to be bad."

Mansoor Al Mahmoud, Qatar Investment Authority's CEO, told CNBC that he's seeing reasons for optimism, despite the state of the global markets right now.

"The sell-off that we see (is) embedded in all of the bad scenarios that we are talking about," he said. "So we're talking about recession, inflation and geopolitical issues."

If there is a downturn, he predicts it will be "light."

"I'm not saying that we will not have a slowdown, I'm not saying that we might not have a recession, but if we have a recession, it will be a light recession," he said.

Citigroup CEO Jane Fraser told CNBC that the war in Ukraine and the developing energy crisis have put the European economy in a precarious position.

"Europe is right in the middle of the storms from supply chains, from the energy crisis, and obviously just the proximity to some of the atrocities that are occurring in Ukraine," she said at the World Economic Forum in May.

When asked if it will lead to recession in Europe, Fraser said "Yes."

The US economy has more resilience, she said, and could avoid a recession altogether, but Fraser told CNBC that will depend on the Federal Reserve's strategy for increasing interest rates.

Speaking at a panel discussion at the World Economic Forum, Nasdaq CEO Adena Friedman said that a culmination of factors would lead to a recession.

"If consumer confidence really continues to go south, the markets continue to show a lot of wobbliness and a lack of a foundation … and that confidence continues to drop, that to me can become self-fulfilling into recession," Friedman, according to the Washington Post. "That's where I see the nonzero [recession] risk."

"It's possible we go into recession, obviously, probably 50-50 odds now," James Gorman, Morgan Stanley's CEO, said June 13 during a conference held by his bank. But, he added, "we're unlikely at this stage to go into a deep or long recession," CNBC reported.

Gorman said he's optimistic that the Federal Reserve will get a handle on inflation and that the economy won't fall into "some massive hole."

But he warned that people will take a hit to their 401k plans.

"You know that it's going to be bumpy," he said.