SYDNEY (Reuters) -Chinese electric vehicle maker BYD said on Tuesday it had raised $5.59 billion in a primary share sale that was increased in size, making it the largest of its kind in Hong Kong in four years.

The company said it sold 129.8 million primary shares in the deal, up from the original 118 million shares planned when the deal launched on Monday.

BYD's Hong Kong shares opened down 8% on Tuesday, in line with the discount the stock was sold at in the deal, while the Hang Seng Index was off 1.5%.

BYD said the transaction was the largest equity follow-on offering globally in the automotive sector in the past decade.

The United Arab Emirates-based Al-Futtaim Family Office was a key investor in the share sale, and the two firms were planning on forming a strategic partnership, BYD said. It did not say how much the family had invested.

BYD sold the shares at HK$335.20 each, a 7.8% discount to the stock's closing price of HK$363.6 on Monday.

The shares were marketed in a price range of HK$333 to HK$345 per share each in the accelerated book build.

BYD's share sale is the largest of its kind in Hong Kong since 2021 when Meituan ( MPNGF ) raised $6.9 billion, according to LSEG data.

The deal reflects increasingly positive sentiment in Hong Kong and China, especially in the tech sector following a high level summit of tech executives led by Chinese President Xi Jinping. China policy makers have also signalled a higher level of support for the country's business private sector.

BYD's Hong Kong shares have risen 36.38% year to date while its Shenzhen-listed listed stock has rallied 27.4% on the back of the improved tech sector sentiment.

The company plans to use the proceeds to invest in research and development, expand overseas businesses, supplement working capital, and for general purposes.

A Citigroup analysis said BYD raising the money offshore in Hong Kong would allow the company to expedite its international business plans.

"BYD has a lot of free cash flow and net cash domestically in China, but it's not flexible and costs a lot to transmit the RMB from China into the currency outside China," Citi analyst Jeff Chung wrote in a research note.

The company is also hampered by having to obtain regular approvals while carrying out capital spending overseas, he said.

Goldman Sachs ( GS ), UBS and CITIC Securities led the BYD deal.