A minor blast on the fifth floor of the District Collectorate building in Kochi, the commercial capital of the state, on Friday afternoon has set the alarm bells ringing in Kerala.

Though there were no casualities, the police have taken a serious note of the incident as the possibility of the blast being a trial run for a bigger show could not be ruled out. Preliminary investigations suggested that a pipe bomb has used for the explosion. Remains of ammonium nitrate, detonators, timer, cable and battery have recovered from the blast site, said the police sources.

Explosives placed among the waste dumped near the stair case at the fifth floor went off at 3 pm. Soon after the blast, the entire floor was evacuated. The building wall had developed minor cracks.

Security for all district administrative offices in the state and other key locations would be strengthened, the sources said. Though no major blast had reported in Kerala yet, there had been incidents of minor blasts, which still remain unsolved.

Today’s blast assumed significance against the backdrop of recent security threats in Kerala, exposure of the state’s terror links with the Valley and arrest of certain Keralites as the prime accused behind major blasts elsewhere in the country.