They may now only issue bonds six months after the previous issue is completed, and an issuance must be completed within 90 days from the date of public announcement of the issue, the recently issued decree, which comes into effect from September 1, stipulates.

Transfers of corporate bonds are also restricted now to 100 times in the first year, though transactions between professional securities companies or done on the order of a court and inheritance do not count toward this limit.

Corporate bonds issued on the international market are exempt from these restrictions.

Another important new regulation is a new issuance plus existing bonds should not exceed 500 percent of the equity value as reported in the latest financial report.

The new decree comes amid a corporate bond boom. According to newly released data by the Hanoi Stock Exchange (HNX), in the first six months of the year there were 130 issuances totally worth over VND156 trillion ($6.73 billion), a 50 percent increase year-on-year.

Financial institutions accounted for 30.29 percent of the value, and the property sector for 29.16 percent.

Businesses’ ability to redeem their bonds on maturity, including those sold to underwriters to meet capital mobilization goals, "wholly depends on the future performance of that company, and so there is a risk of default if the company faces difficulties or goes bankrupt," economist Nguyen Tri Hieu warned.

This risk is exacerbated when companies issue bonds with higher coupon rates than their previous issues just to pay off bank debts or redeem bonds that have reached maturity, he said.

Since the end of 2019 the Ministry of Finance has also been issuing warnings about the potential risks of investing in bonds and telling retail investors "not to purchase bonds just because of high interest rates."

Recently it exhorted bond issuers to carefully calculate their cash flows to ensure they could redeem their bonds when they become due.

SSI estimates the value of outstanding corporate bonds as of June end at VND783 trillion ($33.8 billion), of which around half is held by banks.