A blast hit a police station in the Danish capital, Copenhagen.
This is the 2nd blast to hit the city this week.
On Saturday, the building was damaged but no-one was wounded in the incident early, which took place just outside the city centre.
On Tuesday, there was a powerful explosion outside the national tax agency, in what the authorities say was a deliberate attack.
"This was not an accident, but a deliberate act," Chief Police Inspector Jorgen Bergen Skov said, adding that while the investigation was still underway, nothing suggested it was terror-related.
"These were attacks against buildings, not people," he said. "But it is too early to say anything about the motive."