Three people were killed on Wednesday after, police estimated, a bomb they were in the process of assembling exploded in an apartment on Ben-Zvi street in southern Tel Aviv. Six others were injured in the blast, which police branded a "criminal work accident" and the building was evacuated out of fear it would collapse. Magen David Adom ambulances evacuated the wounded to Wolfson Hospital in Holon and Ichilov Hospital in Tel Aviv. An additional eight people were treated at the scene for minor injuries and shock. Police initially suspected the blast was caused by gas balloons but later announced that it was most probably criminally-related after traces of explosives were found at the scene. Police said the bomb that was being assembled was several kilograms large - the size usually used in underworld assassination attempts. The four-story building suffered serious damages as a result of the blast and contents of the apartment as well as pieces of the building were strewn along the street outside. "The whole building shook and leaned into the street," said Noy - a bystander. "At first I thought the explosion was on a bus underneath the apartment building." The top police brass arrived at the scene of the blast including Internal Security Minister Gideon Ezra. Head of the Tel Aviv District Police Cmdr. David Zur told reporters that police believed the explosion was related to underworld feuds. Zur added that the Tel Aviv Central Investigative Unit - assigned the investigation - would also check the possibility the blast was caused by a bomb planted in or outside the building. Once the dead were identified, Zur said, police would have a clearer picture about what had transpired. "We are not surprised that criminals use explosives and this is not new to us," Zur said. "We do however view the use of explosives very seriously especially when they are found in the middle of a residential area." Several months ago, a known criminal was killed in a similar blast that occurred in a warehouse in Jaffa not far from Wednesday's explosion. Also then police concluded that the explosion was the result of a "work accident" by criminals who were in the midst of assembling a bomb to be used in underworld hits.