The blast took place in a labour department jeep parked in the court premises.
"I rushed out of my office after hearing the noise and saw smoke and fire at the court complex and a vehicle on fire," a woman said.
The police suspect that gun powder was used to trigger the explosion. They recovered 17 batteries and electric fuse and feel a timer was used.
A flying object hit a man on his face after the explosion but his injury was not serious, police sources said.