Pakistan's national grid suffered a major outage on Monday leaving millions of people without electricity. The disruption has begun hitting the country's approximately 40,000 telecommunication towers.

The telecommunication industry source raised fears that if power is not switched back on soon, it could lead to a communications blackout as mobile phone towers run out of backup fuel and batteries.

He added that service degradation had begun in some parts of the country as some towers went offline.

Some social media users in Pakistan complained of mobile signals disappearing in major cities of the country, including Islamabad. "No signals at the Karakoram apartments, Diplomatic Enclave, Islamabad," former Senator Sehar Kamran said on Twitter.

Separately, the country's telecommunication regulator, the Pakistan Telecommunication Authority (PTA), warned of outages.

"Due to country wide power outage, users may face service disruptions," PTA said in a statement.

It said operators have been instructed to inform subscribers and to do their utmost to refuel backup power on the maximum number of mobile tower sites.

A spokesperson for PTA did not respond to a question on how many of Pakistan's telecommunication towers were offline.

Global internet monitoring group Netblocks said on Twitter that metrics showed telecommunications in most regions of the country had been impacted by the country-wide power outage and that there had been a significant decline in internet access.

Pakistan has 194 million cellular subscribers and 124 million broadband subscribers, according to PTA.

There are four major telecommunication providers, including Jazz, owned by Netherlands-based Veon, Zong, owned by China Mobile, and Norway-based Telenor.

(Reporting by Gibran Peshimam and Ariba Shahid, writing by Shivam Patel; Editing by Hugh Lawson)

By Gibran Naiyyar Peshimam