A 5.8 magnitude earthquake struck Burma Sunday evening, hours after a stronger tremor killed at least 13 people and injured 40.
The United States Geological Survey says the quake occurred at a depth of nine kilometres, 86 kilometres north-northwest of the central city of Mandalay.
AFP reporters near the town of Shwebo felt the new tremor.
It came after a more powerful quake sparked panic in the central city of Mandalay.
The shallow 6.8-magnitude quake struck in a rural area 116 kilometres north of Mandalay and was followed by strong aftershocks, the US Geological Survey (USGS) said.
Four labourers flung into the Irrawaddy river from a partly-built bridge near the town of Shwebo, north of Mandalay and nearer to the epicentre of the quake, were among those believed to have died, according to a situation report from Save the Children.
The collapse of a monastery in the nearby village of Kyauk Myaung killed two people and one died in Mandalay, it said.
A further six were killed in Sint Ku township, including two people who died when a gold mine collapsed.
"People everywhere are very worried that another earthquake might strike," the aid organisation said.
Residents of Mandalay fled shaking buildings in terror, although no major damage was reported there.
"I ran from my bed carrying my daughter out to the street. There were many people in the road. Some were shouting and others felt dizzy," Mandalay resident San Yu Kyaw said.
A government official in the capital Naypyidaw who asked not to be named could only confirm two deaths so far.
Another official from Myanmar's Relief and Resettlement Department said that most of those injured were workers on construction sites, with 15 people taken to Shwebo and Kyauk Myaung hospitals.
"We have sent a team to Shwebo where the earthquake was centred to assist in relief works and providing food to the victims," he said.
Save the Children, which has an office in Mandalay, said reports indicated that 25 were injured in the bridge collapse on the Irrawaddy, with 10 taken to hospital.
It said 20 people were thought to have been taken to hospital in Shwebo and a further 10 were being treated in Mandalay.
A large crack stretching from the second to the sixth floor of Mandalay's highest building, the 25-storey Mann Myanmar Plaza, appeared after the quake, a local resident said.
He said people were afraid to enter the structure and it remains closed.
The quake comes little more than a week before US President Barack Obama is due in Burma on a historic visit, as the West begins to roll back sanctions to reward a series of dramatic political reforms under President Thein Sein.
The quake was felt in neighbouring Thailand, including in the capital Bangkok, according to reports on social media websites.
It struck around 572 kilometres east of the Bangladeshi capital of Dhaka, one of the world's biggest cities.
Earthquakes are relatively common in Burma.
Kyaw Kyaw Lwin, an official at the National Earthquake Information Division in the capital Naypyidaw, said it was the strongest quake in the area since a 6.0-magnitude quake in 1991.
More than 70 people were killed in March 2011 when a powerful 6.8-magnitude quake struck Burma near the borders with Thailand and Laos.