A churchgoing family killed in a horrific road smash in California on Tuesday were praised for their 'selflessness and kindness' by those who knew them.

Mario Davila, his wife Maribel and their youngest son, Oscar, 19, were travelling on the 605 Freeway in Whittier when their Nissan was rear-ended by another car, causing it to go on fire with the family still trapped inside.

Police have arrested Los Angeles police officer Edgar Verduzco, who was off-duty at the time of the collision, on suspicion of felony DUI and vehicular manslaughter. His bail stands at $100,000. 

California Highway Patrol said the off-duty officer's 2016 Chevy Camaro crashed into Davila family's Nissan and another vehicle, a 2010 Scion.

The driver of the Scion was treated in hospital for minor injuries, while Verduzco suffered a broken nose.

The California Highway Patrol said in a statement 'it appears alcohol was a factor in this collision with official results pending.' 

LAPD Chief Charlie Beck said he was 'heartbroken' over the family's deaths.

A GoFundMe page has been created to raise funds for the surviving Davila family, which includes three other children.

The page describes Mr and Mrs Davila as being active members of their local community who served at the church they attended, Our Lady of Guadalupe Shrine Church, in Riverside, California.

'Mr & Mrs Davila were people who gave more than they ever took and they passed that lesson down to their kids,' said the fundraising page.

Oscar was described as a 'bright, lighthearted, musically talented individual who, along with his parents served at church.'

'All three of them had positive influences on those around them,' said the page. 'For those who knew them, truly new [sic] them, they couldn't help but gravitate towards them due to their selflessness and kindness.'

So far, nearly $10,000 out of the $15,000 goal has been raised for the gamily since the campaign was set up less than a day ago.