Arsenic has been found in the blood of one of three women who died after eating a Christmas cake in a suspected poisoning in Brazil, a police chief has told local media.

The highly toxic substance was also identified in the blood test results of a 10-year-old boy and the woman who made the cake - both of whom are still in hospital.

Five members of the same family fell ill after eating the cake at a gathering in Torres, in the southern Rio Grande do Sul state, on Monday afternoon.

Police have sent the cake for testing, and said several out-of-date food items were also found during a search at the woman's house. They added that it is not yet clear whether the suspected poisoning was intentional.

Test results from the cake are expected to be available by next week, according to local media.

On Friday, police requested for the body of a man - the late husband of the woman who made the cake - to be exhumed. He died in September from food poisoning, but police said his death was deemed natural at the time.

She is not considered a suspect in either of these cases at this time, and investigations are ongoing.

Six out of seven people at the Christmas celebration ate the cake on Monday afternoon, including the woman who baked it.

Police told Brazilian broadcasters that she is the only one believed to have eaten two slices of her homemade cake, and her tests returned the highest levels of arsenic.

Speaking to local media, police chief Marcos Vinicius Veloso said some of the family members complained that the cake had a "peppery" taste.

The family then began to experience symptoms such as vomiting and diarrhoea, and five of them sought medical help at the Nossa Senhora dos Navegantes Hospital at around 01:00 local time (04:00 GMT) on Tuesday.

Hours later, two sisters died from cardiac arrest, the hospital said. They have been named in local media as Maida Berenice Flores da Silva, 58, and Tatiana Denize Silva dos Santos, 43.

The third victim, whose blood test presented traces of arsenic, died later on Tuesday evening from "shock after food poisoning", the hospital said.

She has been named locally as 65-year-old Neuza Denize Silva dos Anjos.

What is arsenic?

Arsenic is a metallic element that occurs naturally.

Its inorganic form is highly toxic and classified as a category one carcinogen by the EU - meaning it's known to cause cancer in humans.

According to the World Health Organisation (WHO), people are exposed to elevated levels of inorganic arsenic through drinking contaminated water or using it in food preparation, as well as irrigation of crops, industrial processes and smoking tobacco.

Because arsenic exists in soil, small amounts can get into food, though in general, these levels are so low that they are not considered a cause for concern.

It is also used, albeit in limited cases, in pesticides and pharmaceuticals.