A team from the Forensic Science Laboratory is on the spot.
A rocket-propelled grenade or RPG was fired from the street that shattered the glasses at the Punjab Police's intelligence headquarters in Mohali, the police said on Monday.
The police called it an RPG-like attack and termed the blast a minor one.
"A minor explosion was reported at the Punjab Police Intelligence Headquarters in sector 77, SAS Nagar at around 7.45 PM. No damage has been reported. Senior officers are on the spot and an investigation is being done. Forensic teams have been called," the Mohali police said in a statement.
The police have cordoned off the area and an alert has been sounded.
A team from the Forensic Science Laboratory is on the spot.
"The blast took place with a rocket type fire. There is no casualty," said a police official.
"A minor blast took place at the intelligence building. The investigation is going on and our senior officials are on the spot," the police official said.
A quick reaction team of the Chandigarh police was also deputed near the Intelligence office building.