Director General of Police N. Sambasiva Rao said the gun battle occurred during the joint combing operation by special forces of the two states in Malkangiri district of Odisha in the early hours of Monday.
The DGP told reporters that the firing was still continuing and the type of weapons recovered by the police indicate that some top leaders of the Communist Party of India (Maoist), and two women, could be among those killed.
Two commandos of anti-Maoist force Greyhounds were injured in the firing.
He said a helicopter was rushed to the scene to bring the injured personnel and Maoists to Visakhapatnam for treatment.
"We are waiting for more information," the police chief said.
He said the special forces of the two states were combing the area following information about the presence of Maoists.
He said the police asked the Maoists to surrender but they opened fire, forcing the police to retaliate.