A third of the storm-related deaths on the island was caused by issues over access to healthcare, researchers say.

Hurricane Maria killed directly or indirectly more than 4,600 people in Puerto Rico, more than 70 times the toll recorded by officials, a new study has suggested.

In the 102 days since the hurricane hit the island, an estimated 4,645 people died, according to the study published on Tuesday by US-based The New England Journal of Medicine.

A third of the deaths were caused by delayed or interrupted access to healthcare, said the Mortality in Puerto Rico after Hurricane Maria study, which was compiled by Harvard University researchers.

The overall figure dwarfs the government count of 64 people.

It also follows earlier independent studies which placed the death toll at around 1,000 in the 40 days since the hurricane struck.

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Hurricane Maria, the strongest storm to hit the US territory of Puerto Rico in 90 years, made landfall on the island in September 2017.

It caused an estimated $90bn of damages, destroyed more than 70,000 homes and leaving many people with limited access to electricity, fuel, mobile phone coverage and basic supplies.

“On average, households went 84 days without electricity, 64 days without water, and 41 days without cellular telephone coverage after the hurricane,” the study said.

Official toll under review

The latest estimate was based on interviews conducted with more than 3,000 randomly selected Puerto Rican households in January and February this year.

Experts alleged the disruption and widespread devastation hampered attempts to accurately record the number of people killed by the storm.

Puerto Rico officials have not shared any new data on hurricane-related deaths since December 2017, when Governor Ricardo Rossello ordered a review of the official toll.

The study, however, said mortality rates on the island increased 62 percent from September 20 – when Hurricane Maria made landfall – to December 31, compared with the same period in 2016.

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The report used criteria from the US Centers for Disease Control and Prevention (CDC) to determine if a person’s death could be blamed on the hurricane.

Deaths can be attributed to a cyclone if they are caused by forces directly related to the event or unsafe or unhealthy conditions resulting from it, according to CDC criteria.

Accurate recording of the deaths is vital, the study said, for “future risk reduction and preparedness planning”.

At least one independent expert questioned the methods and the number in the new study.

“This estimate could be off by thousands. Easily,” Donald Berry, a professor of biostatistics at the University of Texas MD Anderson Cancer Center, told The Associated Press.

Hurricane Maria was the second Category 5 storm to affect Puerto Rico – home to 3.4 million people – within the space of two weeks last year, after Hurricane Irma killed three people earlier in September.