The wounded have been taken to local hospitals and several were in a critical condition, he said.
The center, which is used by police commandos, is located in a residential neighborhood, he said.
"The scene is ghastly. Limbs and other body parts are strewn all over the place," said Sarat Chandra, a local television reporter present at the blast site.
Imphal is the capital of India's Manipur state, which borders Myanmar.
Dozens of militant separatist groups are active in India's northeast, an isolated region wedged between Bangladesh, Bhutan, China and Myanmar with only a thin corridor connecting it to the rest of India.
Tuesday's bomb attack was the biggest in Imphal in recent times, although the city has been witness to frequent bomb and grenade attacks on government ministers and other government targets.
No one claimed responsibility for Tuesday's blast, Radheshyam said.
The militants say the central government in New Delhi, 1,000 miles to the west, exploits the northeast's natural resources while doing little for the region's indigenous peoples, most of whom are ethnically closer to Burma and China than to the rest of India.
More than 10,000 people have died in separatist violence over the past decade in the region.
