A few unidentified gunmen opened fire inside the Trinamool Congress (TMC) office in the Kharagpur area of West Bengal's West Midnapore district on Wednesday.
Kharagpur Police Control Room confirmed the incident to International Business Times, India.
At least five TMC cadres have been seriously injured. Three of them have been admitted to the Kharagpur Sub-divisional Hospital, while the other two have been taken to the Kharagpur Rail Hospital. Their condition continues to remain critical.
According to local media reports, some have sustained bullet injuries to their stomach, while one person has suffered a head injury.
A police team from the Kharagpur Town police station rushed to the spot after receiving information about the firing and have also launched a manhunt to locate the gunmen.
There are also reports which suggest that the gunmen first threw country-made bombs at the TMC office following which they opened fire. It is also being speculated that the firing could be a result of a feud within the party.