AN artillery strike that hit a refugee camp near Myanmar's border with China has killed at least 29 people, including women and children, media and sources said on Tuesday, in one of the deadliest attacks on civilians since the return of military rule.

Myanmar has been embroiled in a brutal conflict in multiple regions in the wake of a 2021 coup, with ethnic minority armies and a resistance movement battling to undermine military rule after a fierce crackdown by security forces.

Sources including the shadow National Unity Government (NUG) blamed the military for the shelling, which took place close to midnight on Monday in Kachin State.

A spokesperson for the junta said the military was not responsible.

"We are investigating. We always take care of border peace situation," Zaw Min Tun told People Media, adding that the explosion may have involved an ethnic rebel group's own munitions.

Sources said artillery hit a camp for internally displaced people about 5 km (3 miles) from a base in the border town of Laiza run by the Kachin Independence Army (KIA), which has been in conflict for years with Myanmar's military.

Kachin media outlets said 30 people were killed. Reuters could not independently verify the death toll and spokespersons for the KIA could not immediately be reached for comment.

The NUG condemned what it called a vicious attack on civilians and said the world must take action to halt the atrocities and put Myanmar's generals on trial.

"This act of military council is war crime and crime against humanity," NUG spokesperson Kyaw Zaw said, adding an attack at the border with China showed the junta did not respect its neighbour's demand for peace and stability.

The United Nations in Myanmar said on Facebook it was deeply concerned by reports of the incident, adding that "civilians should never be a target".

China's foreign ministry did not immediately respond to a request for comment.

Laiza is the capital of KIA, among the largest of dozens of ethnic groups that have been battling the military for decades.

It sits close to the Chinese border and is home to many civilians living in displacement camps in and around the town. The UN says more than 1 million people have been displaced by the conflict in Myanmar.

A student activist currently in Laiza said the whole town was "shaken" by the explosion and residents were evacuating.

"We are on alert because we worry that there can be second bomb attack," said Justin, who declined to provide a last name. "The locals are worried about that and so people are relocating now."

Kachin media shared a series of graphic images on Facebook of destruction, which could not immediately be verified by Reuters. One showed casualties on the floor, another more than a dozen body bags lined up.

Others showed men in military attire sifting through wreckage and a man carrying the body of a small child.

The incident was the deadliest since an air strike in Myanmar's volatile Sagaing region in April that killed scores of people including civilians.

Khon Ja, a local activist with the Kachin Peace Network Civil society group told Reuters she had visited the local hospital and was told 29 people were dead and 59 wounded.

"The bomb was too strong ... the village was totally destroyed and disappeared," she said.