More than 500 firefighters supported by 20 planes and helicopters were working to bring the blaze under control near the village of Villanueva de Viver, emergency services said on Saturday, forcing 1,500 to leave their homes.
The blaze also spread to the Teruel area of the Aragon region, where 200 people had to be evacuated, authorities said on Saturday.
However, they managed to stop the fire spreading to other areas.
"The surrounding forest has been reached by fire and we don't know how exactly the area looks," Montse Boronat, from Los Calpes, told Reuters.
Ximo Puig, president of the Valencia region, told reporters the blaze was made more "voracious" by summer-like temperatures of about 30 Celsius (86 Fahrenheit).
Las Provincias, a regional newspaper, reported police believe that the blaze may have been started by a spark from a machine used to gather brushwood.
A Spanish Civil Guard spokeswoman said that an investigation was underway into the cause of the fire.
An unusually dry winter across parts of southern Europe has raised concern that there could be a repeat of last year's devastating wildfires.
The weather will be drier and hotter than usual this spring along Spain's northeastern Mediterranean coast, increasing the risk of fires, meteorological agency AEMET said last week.
Last year, some 785,000 hectares were destroyed in Europe, more than double the annual average for the past 16 years, based on European Commission (EC) statistics.
In Spain, 493 fires destroyed a record 307,000 hectares of land, according to the Commission's European Forest Fire Information System.
(Reporting by Graham Keeley, Guillermo Martinez, Miguel Gutierrez, Editing by Jason Neely and Frances Kerry)