Iran has been struck by its most powerful earthquake for more than 50 years, with tremors felt across Pakistan, India and the Middle East.
The epicentre of the 7.8-magnitude quake was near the south-eastern city of Khash, close to Pakistan.
The quake struck deep and in a remote region, apparently limiting casualties.
Iranian state TV said 27 people had been injured, but rowed back on early reports of deaths. More than 30 people were killed in Pakistan.
The area has since been shaken by several strong aftershocks.
Offices were evacuated in Karachi, Pakistan, in the Indian capital of Delhi, and in several Gulf cities.
The earthquake struck in the province of Sistan Baluchistan at about 15:14 local time (10:44 GMT), close to the cities of Khash, which has a population of nearly 180,000, and Saravan, where 250,000 people live.
"The epicentre of the quake was located in the desert, and population centres do not surround it. There were no fatalities in the towns around the epicentre," an Iranian crisis centre official, Morteza Akbarpour, was quoted as saying by the Iranian news agency Isna.
Iranian state TV initially reported that 40 people had been killed, and one Iranian official was quoted by Reuters news agency as saying hundreds of deaths were expected.
Fars news agency said that Saravan had suffered no serious damage.
Across the border in Pakistan, up to 34 people were killed and about 80 injured in the Mashkel district of Balochistan province, the army said.
Communications were disrupted in Mashkel, which has a population of about 45,000. But aid workers said many houses were thought to have been damaged or destroyed.
The earthquake was felt across the region.
Michael Stephens, a researcher at RUSI Qatar, told the BBC from his office in Doha: "I definitely felt the walls shaking. It lasted for about 25 seconds."
Mohammad Wazir, a correspondent for BBC Persian in Pakistan, says the quake was felt in the cities of Karachi and Quetta.
Tuesday's earthquake was about 180 times stronger in energy release than a 6.3-magnitude quake that struck on 10 April near the nuclear plant at Bushehr in south-western Iran. That quake killed at least 37 people and wounded 850.
The Bushehr plant was not damaged by the earlier earthquake, and an official at the Russian firm that built the plant said it had not been damaged by Tuesday's earthquake either, Reuters reported.
Scientists say earthquakes in south-eastern Iran are triggered by the clash between the Arabia and Eurasia tectonic plates, the former of which is pushing north at a rate of several centimetres each year.
In 2003, a 6.6-magnitude quake destroyed much of the south-eastern city of Bam and killed some 26,000 people.