Pakistan's Prime Minister Imran Khan has promised to retaliate against India after it conducted airstrikes on an alleged terrorist training camp across the de facto border in the disputed Kashmir region, in a significant escalation of hostilities between the two nuclear armed powers.

"India has committed uncalled for aggression to which Pakistan shall respond at the time and place of its choosing," Mr Khan's office said in a statement.

The apparent strike took place in the early hours of yesterday morning and came in response to what India said was "credible intelligence" about potential terrorist attacks, Indian foreign secretary Vijay Gokhale told reporters in New Delhi.

Pakistani Prime Minister Imran Khan has vowed to retaliate against India. (Getty)

A National Akali Dal leader shouts slogans in support of India and against Pakistan as he celebrates reports of Indian aircrafts bombing Pakistan territory. (AAP)

An Indian police officer fires a tear smoke shell towards Kashmiri Muslim protesters. (AAP)

Mr Gokhale said the alleged camp was run by Jaish-e-Mohammed, the group India blames for a suicide car bomb attack in Pulwama in Indian administered Kashmir that killed 40 Indian paramilitary soldiers on February 14.

It was the worst attack on Indian forces since the beginning of an insurgency in the region in the late 1980s, according to analysts.

At an election rally a few hours after the airstrikes, Indian Prime Minister Narendra Modi did not refer to the attack directly, but spoke about protecting India.

"I want to assure my countrymen that the country is in safe hands," he said.

The Indian government had been weighing up how to respond to February's terror attack in Indian-administered Kashmir, conducting raids over the past two weeks to weed out militants hiding in the region.

Protesters burn an effigy of Indian Prime Minister Narendra Modi in Peshawar, Pakistan. (EPA/AAP)

A photo released by Pakistani military authorities showing the purported scene of the airstrike. (EPA/AAP)

Indian people shout patriotic slogans and fire crakers as they celebrate the Indian Air Force's air strike across the Line of Control near the international border with Pakistan. (AAP)

Harsh V. Pant, a professor in international relations at King's College London, told CNN that for the past few decades the Indian government had chosen not to retaliate after terror attacks in Kashmir.

But India is now at a point where it is choosing to escalate the situation, he said.

A spokesman for the Pakistan Armed Forces tweeted that Indian military aircraft crossed into Pakistan airspace, but were driven back.

Pakistan Major General Asif Ghafoor alleged that Indian jets crossed the LoC and were pushed back by Pakistan Air Force jets that were "scrambled" to the scene.

"Indian (aircraft) intruded from Muzafarabad sector. Facing timely and effective response from Pakistan Air Force released payload in haste while escaping which fell near Balakot," Maj. Gen. Ghafoor said in a statement posted on his official Twitter account.

In a statement, India said "a very large number" of militants were "eliminated" in the operation.

An Indian paramilitary soldier uses a sling to throw a stone at Kashmiri Muslim protestors. (AAP)

It said the alleged camp was a military training facility headed by Maulana Yousuf Azhar, the brother-in-law of Masood Azhar - the chief of Jaish-e-Mohammed.

Pakistan denied that numerous militants had been killed, calling it "a self-serving, reckless and fictitious claim" by the Indian government, according to the statement from Mr Khan's office.

"This action has been done for domestic consumption being in election environment, putting regional peace and stability at grave risk," the statement read.

The movement of Indian Air Force planes across the de facto border between the two countries is the first such instance since the India-Pakistan war in 1971, Mr Pant said.

India has previously claimed Pakistan had a "direct hand" in the Pulwama bombing.

"It is a well-known fact that Jaish-e-Mohammed and its leader Masood Azhar are based in Pakistan. These should be sufficient proof for Pakistan to take action," India's Foreign Ministry said in a statement posted February 19.

Following the attack, India promised retaliation, including commercial and diplomatic steps to "isolate" Pakistan internationally.

"There has been diplomatic outreach [by India] to various countries," Mr Pant told CNN.

He said India's military action follows public anger over the attack.

Pakistan has vehemently denied having a role in the incident.

China called on both countries to "exercise restraint" after news of the airstrikes broke.

"Both India and Pakistan are important countries in South Asia," China's Foreign Ministry spokesperson Lu Kang said during a daily press briefing.

"We hope that both sides can exercise restraint, and take actions that can contribute to the region's stability and improve their mutual relationship, but not the opposite."

Pakistan's information minister, Fawad Hussain, has asked the country's media regulator to ban Indian advertisements and said in a Twitter post that Pakistan's association of cinema exhibitors will boycott Indian movies.

Back in 2016, rising military tensions between both countries also led to a ban on Indian movies and shows in Pakistan.

Meanwhile, India is mulling a boycott of their Cricket World Cup showdown against Pakistan in the UK this June.

The Board of Control for Cricket in India issued a statement last week in which it urged "the cricketing community to sever ties with countries from which terrorism emanates."

Kashmir, a largely mountainous region located between India and Pakistan, has had a tumultuous history.

The region has been bitterly contested by both India and Pakistan following the partition of the two countries in 1947, leading to three wars and numerous other skirmishes.

The February attack came more than two years after armed militants entered an Indian army base in the garrison town of Uri, about 102 kilometres from Srinagar - killing 18.

India later said it had used ground troops to strike terrorist targets across the Line of Control in response to the Uri attack, something which Pakistan denied.

Days after February's attack four Indian army personnel were killed in a gunfight with militants in the Pulwama district of Indian-administered Kashmir.

Separatist violence in the region has killed more than 47,000 people since 1989, although this toll doesn't include people who have disappeared due to the conflict.