On Monday morning, Merseyside Police said 21 fire engines were still battling the blaze, with the fire service adding that the fire is now contained to the auto park.
Most of the vehicles belonged to visitors to the city's International Horse Show at the arena, who were left stranded overnight.
There were no reported injuries in the blaze.
"It was frightening. We could hear the bangs of auto windows exploding", he said.
A number of animals appearing in The Horse Of The Year Show at the Echo Arena were safely taken from the scene.
Chief Merseyside Fire and Rescue Service Officer Dan Stephens said tightened budgets meant large fires presented huge challenges.
An old Land Rover with its engine on fire is thought by firefighters to be the source of the blaze.
She described how the horses were brought into the arena to keep them safe, including some that had been safely removed from the ground floor of the vehicle park.
There was an global horse show scheduled to take place at the Liverpool Echo Arena, next to the auto park, which was cancelled.
He said: "A fireman said the whole vehicle park is on fire".
Ms Hughes, who had gone to the event with her daughter, said the consequences of the fire "could have been a heck of a lot worse".
The city council opened an emergency relief centre in a local gym to accommodate those without transport and also residents of a nearby block of flats which had to be evacuated due to danger from smoke. Although crews attended within eight minutes of the alarm, the flames spread so quickly they were not able to control the blaze, he added.
The Home Office said Fire and Rescue services had the resources to do their work and Mersyside's service will see an increase in core spending of 0.9% in the coming year.