In the 50s (up til 1972), the US led a total embargo on China, including a food and fertilizer embargo in the express goal of causing a famine that would lead to regime change. By 1959, China’s grain reserves were low and production was not capable of keeping up. It was clear to the CCP that things were heading to an upcoming famine, without imports to cushion the upcoming deficit. Here’s a breakdown of the factors:

• Poor weather leading to poor crop yields. This was the biggest factor despite mainstream rhetoric both in China and abroad: «The Economic Situation in Communist China», Apr 4 1961. https://www.cia.gov/readingroom/docs/DOC_0001098172.pdf (p.3 paragraph 13, or p.5 of pdf file). Both the West and Chinese successors of Mao (who were of an opposing faction to him) have very good political reasons to blame him for everything.
• Bad policies leading to poor crop yields: the infamous Four Pest Campaign. While not the main factor for the poor crop yield as modern rhetoric claims, it remained a significant factor. (Same CIA document addresses this in paragraph 14)
• Rampant population growth. The same CIA document, in paragraph 9, notes that agricultural production actually increased in China from 168 to 185 million tons, just not enough to keep up with population growth
• Bad policies leading to poor grain reserves: in 1958, (same CIA document, paragraph 9), grain production increased to 212 million tons. However, CCP allowed free supply of food in the communes’ mess halls instead of its usual rationing, which led to depleting reserves instead of padding it despite a good year.
• Bad policies leading to poor grain reserves: as a rule, China was a food exporter instead of a food importer in the 50s prior to the famine, as it required capital for its industrialization and had little else to offer that other nations would buy. This wasn’t an inherently bad tradeoff (a similar kind of tradeoff would lead to China’s rise as a nation), but became one due to CCP not keeping enough grain reserves that could account for 3 consecutive bad years.

It was therefore in 1959 that the CCP started negotiating grain purchases with Western nations that had a surplus, but they were resisting at that point due to US-led embargo. (The US put significant pressure on its allies to comply with the embargo) https://www.theglobeandmail.com/news/national/an-era-ends-as-china-becomes-an-aid-donor/article978192/ (paywall. Mirror: https://archive.is/9Ksoq). The famine happened as engineered by the US despite CCP’s efforts in preventing it (both in attempting to purchase grain and in transporting their available food around to lower death toll). Death tolls are likely exaggerated (all state actors around the world had reason to, again due to political expediency vis-à-vis Mao), but the famine did indeed happen. The lowest estimates are around 5 million (figure Mao gave to US diplomats), up to 30 something million (extremely unlikely).

After the famine worsened in winter 1961, Canada and Australia had enough of being complicit in genocide and decided to defy the US embargo and sent China grain (both paid and given). This was sufficient to stop the famine and bought them considerable goodwill from the PRC for a few decades. At this point, the CIA calculated that if Canadian and Australian grain imports stopped, it would be enough to send China back into the worst parts of the famine (thereby confirming that if grain imports started in 1959, there wouldn’t have been a famine to begin with). It then lamented at the poor cooperation of US allies in this attempted genocide in the CIA report «Communist China: Economic Performance in 1962», Dec 3 1962. https://www.cia.gov/readingroom/docs/DOC_0000402879.pdf (p.8-9; or p.10-11 of pdf file).

Side note that doesn’t really affect how the events unfolded in either CCP actions nor US intentions: In February 1961, the CCP expressed a need for urgent grain purchases to the Soviet Union. Khrushchev offered 1 million tons of grain and half a million tons of Cuban sugar on a loan basis. China agreed to use the sugar loan and asked to keep the grain offer in reserve (Lorentz M. Lüthi’s book «The Sino-Soviet Split»). It then however used part of the offer soon after (200 000 tons, according to Barbara Barnouin in «Zhou Enlai: A Political Life»). This was shortly before the Sino-Soviet split was complete. The loan was paid back with Canadian grain. That China negotiated for grain from Canada in 1959, and only from the Soviets in 1961 after the famine got really bad, spoke volumes about how bad Sino-Soviet relations were at that point. Also, it is probably slightly unfair to say that CCP successors to Mao blamed him solely for political expediency; there was good grounds to say if CCP did not make the numerous poor policy decisions listed above, the famine may not have happened (or at least not have been as bad) despite the poor weather and the US genocide attempt. CCP is inherently pragmatic and considers being able to weather both natural disasters and hostile factors its mandate. This was likely a large part of why it declared the GLF famine “mostly man-made [by itself]” despite the fact that the men that intentionally made the famine were in Washington and not Beijing.

from the linked CIA doc:

Failure to import 5 million mt of grain in 1963 might reduce by 3 to 4 percent the total caloric availability, thereby diminishing labor productivity … and causing increased rural dissatisfaction. … The cumulative effects of prolonged malnutrition … could lead to a level of unrest that would tax the police powers of the regime.