The epicentre of Tuesday's 7.8-magnitude quake lay in south-east Iran but all 40 deaths reported so far have been across the border in Pakistan's dirt-poor province of Baluchistan, where hundreds of mud-built homes suffered damage.

The powerful tremor shook the ground and caused panic as far afield as Kuwait and the Indian capital New Delhi. Thousands of people evacuated towering residential and office buildings in Dubai.

A new aftershock early on Wednesday frayed locals' nerves on the Iran-Pakistan border. The US Geological Survey measured its magnitude at 5.7.

In Pakistan, officials said that regular army and paramilitary forces had deployed to help the relief effort after Tuesday's quake brought down homes in the Mashkail area of Baluchistan.

Military helicopters carrying medical teams have been sent to the area while paramilitary troops are supplementing the relief efforts, they said.

"The death toll is estimated at more than 40, including women and children," Major Attiq Minhasof from the paramilitary Frontier Corps Baluchistan told Agence France-Presse (AFP) at Dalbandin airport, around 250 kilometres from Mashkail.

650 personnel involved

He said 650 personnel were involved in the rescue operation in Mashkail town and that so far medical staff had received 23 wounded people.

Abdul Bari, a 32-year-old tailor who broke his leg, told AFP that his wife and children were fine, but feared that dozens of people from his neighbourhood had been killed or wounded.

"I was on my way home from my tailoring shop when the earth started shaking and soon found myself on the ground with the wall of a house on me," he told AFP in Dalbandin, after travelling for five and a half hours by taxi for help.

"When I felt the tremors, I saw within seconds houses razed to the ground. It was like doomsday," he said, while waiting for an army helicopter ambulance.

"I saw three small children taken out from the debris of a collapsed wall by local people. Two were slightly injured while one seemed serious," he added.

Baluchistan, an inaccessible province bordering Iran and Afghanistan, is plagued by Islamist militancy, attacks on the Shiite Muslim minority and a separatist Baluch insurgency.

Putting aside America's longstanding enmity with Iran, and its more recent strains in relations with Pakistan, US Secretary of State John Kerry offered "our deepest condolences" to the families of the dead and to the injured.

"We stand ready to offer assistance in this difficult time," he said.

US disaster diplomacy with Pakistan

Disaster relief contributed to an earlier thaw in relations between the United States and Iran, which – then led by reformist president Mohammad Khatami – accepted US personnel following the huge Bam earthquake in 2003.

The United States has also engaged in disaster diplomacy with Pakistan, briefly improving its abysmal image in the country through a robust relief operation following a 2005 earthquake in Pakistani-administered Kashmir.

The Bam quake killed more than 26 000 people, while more than 73 000 died in the Kashmir one.

UN chief Ban Ki-moon also expressed condolences after Tuesday's disaster and said the "United Nations stands ready to help as necessary if asked to do so".

The quake struck in the afternoon with its epicentre around 80 kilometres east of the city of Khash, in the Iranian province of Sistan Baluchistan, the US Geological Survey said.

A local health official in Iran told the Fars news agency that more than 20 villages were probably "severely damaged", based on initial reports.

27 people hurt in Iran

At least 27 people were hurt in Iran, according to a local governor speaking to the IRNA news agency, but there was no immediate confirmation of any deaths.

The quake came a week after another struck near Iran's Gulf port city of Bushehr, killing at least 30 people.

The International Atomic Energy Agency reported that the latest quake had caused no damage to Iran's nuclear power plant at Bushehr or any other nuclear facilities.

David Rothery, who chairs the volcanoes, earthquakes and tsunamis course at Britain's Open University, said the depth of Tuesday's quake – 82 kilometres underground – would have lessened its impact.

But he added that the area "is mountainous, and damage can be expected from landslides as well as because of poorly constructed buildings". – AFP