A magnitude 7.8 earthquake has struck southeastern Iran near the border with Pakistan, reportedly killing at least 15 people, with casualties feared to rise, according multiple news sources.
The US Geological Survey said on Tuesday that the epicentre of the quake was 86km southeast of Khash, Iran.
According to the Iranian FARS news agency, several people were killed in the sparsely populated region.
An Iranian government official said on he feared more casualties from the earthquake.
"It was the biggest earthquake in Iran in 40 years and we are expecting hundreds of dead," the official, who spoke on condition of anonymity, told Reuters.
A resident in the quake zone, Manouchehr Karimi, told AP by phone that "the quake period was long'' and occurred "when many people were at home to take a midday nap".
In Panjgur in the Pakistan state of Balochistan, five more people were confirmed killed, Balochistan home secretary told Al Jazeera's Osama Bin Javaid. In a village called Mashkel, dozens of mud houses have reportedly collapsed.
Another Al Jazeera correspondent in Pakistan also quoted "eye witnesses" as saying that thousands of homes were "fully destroyed" in areas near Iran's border with Pakistan.
Al Jazeera's Saira Jaffer, reporting from Islamabad, said tremors were also felt across Karachi and Balochistan.
Many buildings in Karachi were reportedly evacuated.
In the Indian capital New Delhi, tall buildings shook sending people running into the streets, witnesses told Reuters.
Across the Gulf, people also evacuated shaking buildings in Qatar and Dubai, residents said. Dubai has the world's tallest tower, the 828-metre Burj Khalifa.
Last week, a 6.3 magnitude earthquake also hit Iran killing at least 37 people and injuring 850 more in the country's southwest.
In December 2003, a big earthquake struck the southern city of Bam. It killed 31,000 people - about a quarter of the population - and destroyed the city's ancient mud-built citadel.