WELLINGTON -- New Zealand reported its first recorded death linked to U.S. drugmaker Pfizer's COVID-19 vaccine, the health ministry said on Monday, after a woman suffered a rare side-effect leading to inflammation of the heart muscle.

The report comes as the country battles an outbreak of the Delta variant after nearly six months of being virus free. It followed a review by an independent panel monitoring the safety of the vaccines.

"This is the first case in New Zealand where a death in the days following vaccination has been linked to the Pfizer COVID-19 vaccine," the ministry said in a statement, without giving the woman's age.

The vaccine monitoring panel attributed the death to myocarditis, a rare, but known, side-effect of the Pfizer vaccine, the ministry added.

Myocarditis is an inflammation of the heart muscle that can limit the organ's ability to pump blood and can cause changes in heartbeat rhythms.

Pfizer said it  recognized there could be rare reports of myocarditis after vaccinations, but such side-effects were extremely rare.

"Pfizer takes adverse events that are potentially associated with our vaccine very seriously," it told Reuters.

"We closely monitor all such events and collect relevant information to share with worldwide regulatory authorities."  

The health ministry said other medical issues at the same time could have influenced the outcome after vaccination.

But the vaccine's benefit outstripped risks from side effects, it added.

"The benefits of vaccination with the Pfizer COVID-19 vaccine continue to greatly outweigh the risk of both COVID-19 infection and vaccine side-effects, including myocarditis."

Regulators in the United States, the European Union and the World Health Organization have said that mRNA vaccines by Pfizer and partner BioNTech and by Moderna are associated with rare cases of inflammation of the heart muscle or of the lining around the heart but that the benefits outweighed any risks.

The cases, affecting mainly younger men, tend to be mild and are treatable but can lead to serious illness, WHO has said.

The EU's drug regulator said on July 9 that five people had died due to the side-effect after receiving either of the two mRNA vaccines in the European Economic Area, all of whom were elderly or had other diseases. More than 200 million mRNA doses have been administered in the region.

New Zealand has provisionally approved use of the Pfizer/BioNTech, Janssen and AstraZeneca vaccines, but only the Pfizer-produced vaccine has been approved for rollout to the public.

Monday's 53 new cases took New Zealand's tally of infections in the current outbreak to 562, amid a nationwide lockdown enforced this month to limit spread of the Delta variant.