A California family has been torn apart across three generations after a man allegedly set their home ablaze, killing his own father, sister, and her two young children.

Sergio Ivan Rivera-Vega, 32, is accused of intentionally starting the devastating Richmond house fire on Tuesday night that claimed the lives of his father Jose Rivera, 47, his nephew Andrew, five, and his niece Joline, who was just two.

The children's 33-year-old mother Maria, who is Rivera-Vega's sister, was also critically injured in the inferno and later died from her injuries.

Rivera-Vega now faces four counts of murder as a result of the horrifying blaze that ripped through the family's home on Tuesday night.

The tragedy has left surviving relatives both grieving four members of their family and confronting the destruction of the home they shared.

'My mom and I are heartbroken and overwhelmed trying to process so much loss all at once,' Rivera-Vega's sister Evelin Rivera wrote in an GoFundMe page.

'We urgently need help with funeral services and burial expenses for my dad, my niece, and my nephew.'

The deadly fire was reported at around 9pm on Tuesday with Rivera-Vega identified by police as the person they believe intentionally ignited the blaze.

He was arrested the following day and booked into the Martinez Detention Facility.

Authorities have not publicly revealed what they believe drove him to allegedly set fire to a home containing his own relatives.

Contra Costa County District Attorney Diana Becton described the deaths as a staggering loss made even more difficult to comprehend because of the relationship between the accused man and those who died.

'This fire is devastating for the entire family,' Becton said. 'Knowing the suspect is related to the victims - including two children - makes this loss even harder to comprehend this senseless act.'

The youngest victims were just two and five years old.

Andrew and Joline were Jose Rivera's grandchildren and Rivera-Vega's nephew and niece.

By Sunday morning, a fundraiser for funeral and burial costs had collected almost $70,000.

In the online appeal, Rivera-Vega's younger brother described a family suddenly left without a home and struggling to meet everyday expenses.

'My mom, siblings and I are heartbroken and overwhelmed trying to process the loss of our loved ones,' he wrote. 'We are asking for help with living expenses, after our home was destroyed in that tragic fire.'

He said he was unemployed and struggling to help his surviving relatives pay their basic bills.

'Any donation or share would mean so much to our family as we try to rebuild our lives.'

As investigators work to establish what led to the fire, relatives have begun describing the family tensions that allegedly preceded it.

Anselmo Rivera, Jose's brother and Rivera-Vega's uncle, told KTVU that the accused man had struggled with mental health issues.

He also alleged that Rivera-Vega had made verbal threats against members of the family during the previous month.

Anselmo paid tribute to his brother as a generous, hardworking man who devoted himself to supporting his family.

'My brother was special... a very nice person,' Anselmo said. 'Anybody who come and asks him for something, he always says yes.'

Jose worked hard in construction to provide for those around him, his brother said.

'I miss him,' Anselmo said. 'I feel very bad for him.'

Rivera-Vega was charged Friday by the Contra Costa County District Attorney's Office with three counts of murder with special enhancements.

His bail was set at $2.5 million and he will be arraigned on Monday.