One person was also missing after the explosion which sent a pall of smoke billowing over the car park where the car blew up at around 11 a.m. (1000 GMT).
The force of the blast shattered windows at a university building and damaged nearby cars.
"We were lucky with the weather. It's cold and wet and fewer people than usual were walking around the car park,"
"We are looking for a worker who was supposed to be inside the building. She clocked in and we can't find her," Barcina said.
Basque Country police said a warning call had been received before the explosion but it did not specify where the bomb was.
Another university building was evacuated after a second call was received following the explosion, Spanish state radio said.
The blast came just two days after Spanish police arrested four suspected ETA guerrillas they said had been planning attacks in the
ETA has killed more than 800 people in four decades of armed struggle for independence of ancient Basque territories in
Authorities blamed the separatists for two bomb attacks which caused no casualties over the weekend in the Basque Country.