Hong Kong's Security Secretary John Lee said on Wednesday the Chinese-ruled city was facing the risk of "home-grown terrorism" after several police reports of finding explosive materials.
It was unclear whether any of the incidents were related to the anti-government protests that rattled Hong Kong last year before pausing in recent months amid social distancing adopted to prevent the spread of the coronavirus.
The latest incident involved a suspected small, homemade explosive device mailed in an envelope to police headquarters, police said, adding it could have injured anyone within one metre (3 ft).
Police said the explosive ordinances disposal team dealt with the device and evacuation was deemed unnecessary.
In recent months, police said they had discovered explosive substances and devices across the city, including in a downtown school and on train tracks near the mainland border. They said some homemade devices were discovered at protests sites last year and during raids of homes where protesters were arrested.
"I want to remind people of the risk of rising home-grown terrorism," Lee told reporters. "Some might die because of bombs, buildings might be demolished."
"I asked police and other law enforcement agencies to strengthen the work related to that," Lee said, adding that this could include using terrorism financing legislation to freeze the assets of those involved.
Critics say authorities in Hong Kong and Beijing are increasingly using the threat of what they call terrorism to justify calls for new national security laws.
A previous attempt to draft a national security law for Hong Kong, known as Article 23, was met with mass protests in 2003 amid fears it would limit the city's freedoms. It was abandoned.