"Many of the tourists got trapped under the overturned boat and died of suffocation", said one of them.
The police had also informed that nine people had drowned in Vaishali.
According to Vijayawada police, the motor boat with a three-man crew was ferrying 38 passengers from Bhavani Island to Pavitra Sangamam near Ibrahimpatnam on the outskirts of Vijayawada for a religious ceremony on Karthika Masam.
More than 16 people were killed when the boat in which they were travelling capsized at Pavithra Sanghamam near Vijayawada. Swimmers and local fishermen rescued 15 passengers as the boat capsized.
Around 20 of the roughly 35 people on the boat were rescued and search operations were continuing, India's National Disaster Response Force said on Twitter. Of them, 32 belonged to a walkers' association from Ongole in Prakasam district and six from Nellore.
Later, 16 bodies were fished out of the river.
Sixty members of the NDRF and 60 members of fire department with 12 boats participated in the rescue operation.
Chief Minister N Chandrababu Naidu expressed his grief over the incident, and asked the District Collector and police authorities to take the necessary action. He announced Rs 8 lakh compensation each to the families of the deceased.
Pradesh Congress Committee president N Raghuveera Reddy visited the accident spot and later the hospital.