In the town of Madhopur, on the border between Punjab state and Kashmir, police stopped about 3,000 BJP activists from crossing a bridge on their way to Srinagar.
"We will not allow anyone to enter Kashmir today. All borders have been sealed and highways are blocked," Gareeb Das, a senior police officer stationed in Madhopur, told the AFP news agency.
"Multi-tearshell launcher vehicles and water cannons have been deployed at all entry points."
The Bharatiya Janata Party (BJP) called for Hindu volunteers to go the Muslim-majority region to raise the national flag in region’s main city, Srinagar, on Wednesday for India's Republic Day.
Officials are concerned that this would trigger major unrest in the region, where there is a long and ongoing violent separatist uprising.
But despite the police blocking entry to Kashmir, the BJP said it was determined to get to Srinagar.
"No one has the right to stop us from hoisting the Indian flag in Kashmir. We will not change our plan," Anurag Thakur, president of Bharatiya Janata Yuva Morcha, the youth wing of the BJP, told AFP.
Pro-independence Kashmiris said they would protest on Republic Day, raising fears of violence. Massive anti-India protests last year left dozens of protesters dead.