Blasts were heard in Srinagar and Jammu and projectiles and flashes were seen in the night sky over Jammu, similar to the events of the previous evening, according to authorities, residents and Reuters witnesses.
Indian Foreign Secretary Vikram Misri said Pakistan had violated the understanding arrived at by the two countries earlier in the day.
"We call upon Pakistan to take appropriate steps to address these violations and deal with the situation with seriousness and responsibility," Misri told a media briefing.
Pakistani Information Minister Attaullah Tarar told broadcaster Geo News: "As of now, there have not been any ceasefire violations."
The fighting had been the worst between the old enemies in nearly three decades and threatened to erupt into a full-scale war in one of the world's most volatile and densely populated regions.
There were briefly fears that nuclear arsenals might come into play as Pakistan's military said a top body overseeing its nuclear weapons would meet.
But the defence minister said no such meeting was scheduled, hours after a night of heavy fighting in which the two countries targeted each other's military bases and the combined civilian death toll rose to 66.
"Pakistan and India have agreed to a ceasefire with immediate effect," Foreign Minister Ishaq Dar posted on X.
"Pakistan has always strived for peace and security in the region, without compromising on its sovereignty and territorial integrity!"
Misri had earlier said the two countries' military operations chiefs had spoken to each other and agreed that all fighting would stop at 5pm Indian time, without using the word "ceasefire".
US President Donald Trump posted: "After a long night of talks mediated by the United States, I am pleased to announce that India and Pakistan have agreed to a FULL AND IMMEDIATE CEASEFIRE. Congratulations to both Countries on using Common Sense and Great Intelligence."
Dar told the broadcaster Geo News that military channels and hotlines between India and Pakistan had been activated, and three dozen countries including Saudi Arabia and Turkey had helped to facilitate the agreement.
On Wednesday, India had attacked what it said was "terrorist infrastructure" in Pakistani Kashmir and Pakistan, two weeks after 26 people were killed in an attack on Hindu tourists in Indian Kashmir.
Pakistan denied India's accusations that it was involved in the attack.
Days of cross-border fire, shelling and drone and missile attacks followed.
US Secretary of State Marco Rubio said that he and Vice President JD Vance had engaged with Indian Prime Minister Narendra Modi and Pakistan's Shehbaz Sharif, Indian Foreign Minister Subrahmanyam Jaishankar, Pakistan's army chief Asim Munir, and the two national security advisors over the course of 48 hours.
In a post on X, Rubio commended Modi and Sharif on the agreement, which he said included not only an immediate ceasefire but also the start of talks on "a broad set of issues at a neutral site".
News of the ceasefire was greeted with relief on both sides of the border and Pakistan's airports authority said its airspace had been fully reopened.
But the subsequent violations sparked alarm in India.
"What the hell just happened to the ceasefire? Explosions heard across Srinagar!!!", Omar Abdullah, chief minister of Indian Kashmir, posted on X.
"This is no ceasefire. The air defence units in the middle of Srinagar just opened up."
India and Pakistan have been locked in a dispute over Kashmir ever since they were born at the end of British colonial rule in 1947.
Hindu-majority India and Muslim Pakistan both rule part of Kashmir but claim it in full.
India blames Pakistan for an insurgency in its part of Kashmir that began in 1989 and has killed tens of thousands.
It also blames Pakistani Islamist militant groups for attacks elsewhere in India.
Pakistan rejects both charges and says it only provides moral, political and diplomatic support to Kashmiri separatists.
with AP
