Witness relates trauma in Anders Behring Breivik trial
Tor Inge Kristoffersen told the Oslo court he watched on CCTV as a car parked and a man wearing what looked like a guard's uniform got out.
Mr Kristoffersen said he zoomed in on the number plate before the vehicle exploded killing eight people.
Breivik has admitted the bombing and subsequent shootings on Utoeya island.
During his evidence Mr Kristoffersen said, "Half of our screens, the images disappeared. There was a deep rumbling, the entire block shook, the ceiling bent like water."
Mr Kristoffersen also spoke of one colleague who died in the blast, and of others who were no longer able to work as a result of the psychological effects of the bombing.
A second witness, civil engineer Svein Olav Christensen, has also been giving evidence on the impact of the explosion.
He showed a picture of a 2m-wide hole created by the bomb that went straight down into the underground parking area.
Anders Behring Breivik watched the witnesses in court without any visible emotion.
He spent the past week giving his own version of events, saying his plan was to kill as many people as possible.
He said he had hoped the car bomb would cause the whole government building to collapse.
After the explosion he went to Utoeya island where he killed a further 69 people at a Labour Party youth camp.
Breivik denies insanity
He denies criminal responsibility for the killings, saying he was defending Norway from multiculturalism.
The trial in Oslo will decide whether he is sane. A state psychiatric commission requested further clarification on the second of two psychiatric reports, which concluded he was sane and accountable for his actions.
The first report found him legally insane.
Depending on whether he is found sane or not, he faces either prison or committal to a psychiatric institution.
Mr Breivik said he would do "anything to prevent" committal to a hospital.
Breivik was allocated five days in total to give evidence, with the entire proceedings expected to last 10 weeks.
