At least 30 people have been killed in a region on Myanmar's border with China after rebels - some dressed in police uniforms - launched a surprise attack, according to authorities.

Monday's clashes were some of the worst to break out in the Chinese-speaking Kokang region of the northeastern state of Shan since fighting in 2015 left scores dead and forced tens of thousands to flee across the border into China.

Rebels from the Myanmar Nationalities Democratic Alliance Army (MNDAA) group launched an attack early on Monday against police and military posts in Kokang, according to the office of Aung San Suu Kyi, Myanmar's de facto leader.

A separate group of fighters later attacked locations in Laukkai, a main town in Kokang.

"According to initial information, many innocent civilians including a primary school teacher ... were killed because of attacks by the MNDAA armed group," the state counsellor's office said in a statement.

It also said some attackers wore local police uniforms.

The statement, accompanied by graphic pictures of the dead and wounded, said at least five civilians and five local police were killed in the fighting.

It also said that a further 20 "burned bodies" had been found alongside weapons.

Zaw Htay, the government spokesman, told AFP news agency that the 20 bodies were of MNDAA fighters.

Unverified video shared on social media appeared to show parts of the town still ablaze on Monday afternoon while civilians scurried to safety amid the rattle of small arms fire.

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An army source told AFP that the fighting was continuing as darkness fell.

"Residents in town are fleeing. We do not know exact figures yet," the officer said.

The Northern Alliance, an umbrella group of rebels including the MNDAA which has yet to join national peace talks, confirmed its members were fighting in Laukkai.

But in a Facebook post, it said they carried out the attack "to resist an enemy offensive in self-defence" and cited Myanmar military operations since December.

Multiple conflicts

Myanmar is torn by multiple ethnic conflicts, but the Kokang conflict has raised tensions with China.

The latest fighting raises the spectre of a fresh refugee exodus into China.

In early 2015 tens of thousands fled there when dozens of civilians, rebels and army troops died in months of fighting across the remote and mountainous region.

IN PICTURES: Displaced by continued fighting in Myanmar's Shan state

China said Myanmar warplanes dropped bombs on its side of the border during that bout of fighting.

Kokang has strong bonds with China - local people speak a Chinese dialect and China's yuan is the common currency.

Observers say China's government holds considerable sway over the rebels.

Clashes with the Northern Alliance have intensified across Shan state since late last year, claiming more than 160 lives across an arc of land in the long border region.