The sale, which came days before the car maker said its January-June profit tripled compared with a year ago, reduced Berkshire’s holdings in BYD from 220 million shares to 218.7 million shares, according to the filing.

The investment firm’s 2021 annual report put Berkshire’s stake in BYD at about 225 million shares, or 7.7% of the company, reflecting shares listed in Hong Kong as well as Shenzhen and elsewhere. It couldn’t be determined why the stock exchange filing put the firm’s holdings at 220 million shares before the sale or when Berkshire’s holding was reduced by 5 million shares.

In 2008, Berkshire paid $230 million for a 10% stake in BYD.

BYD and Berkshire didn’t immediately respond to a request for comment.

BYD’s Hong Kong-listed shares slumped 11% in Wednesday morning trading to their lowest level since mid-May.

The Shenzhen-based auto company’s net profit attributable to ordinary shareholders in the first six months of this year soared to about 3.6 billion yuan, equivalent to around $520 million, from 1.2 billion yuan a year earlier, according to its earnings report filed Tuesday. The company releases earnings reports every six months.

Robust growth in its car sales drove up BYD’s revenue by 66% to 151 billion yuan. The car maker remained unscathed even as Covid-19-related city lockdowns and supply-chain disruptions plagued parts of China in March and April, crippling some rivals’ car deliveries, including

Tesla Inc.’s

.

In a pivot to selling electric cars, BYD said it stopped producing traditional combustion-engine vehicles in March. The company sold 324,000 battery cars globally and about 315,000 plug-in hybrid electric cars in the six months through June.

—Akane Otani

contributed to this article.

Corrections & Amplifications
Berkshire Hathaway Inc. sold 1.33 million of BYD Co.’s Hong Kong-listed shares at an average of 277.10 Hong Kong dollars a share, equivalent to around $35 a share. An earlier version of this article incorrectly said that 277.10 Hong Kong dollars was equivalent to around $29 a share. (Corrected on Aug. 30)

Write to Selina Cheng at selina.cheng@wsj.com