Ethiopian authorities have arrested people connected to "the security crisis in Amhara", the government said after imposing a state of emergency on the northern region following clashes between local fighters and federal troops.

On Saturday, the government communications service said those who "exacerbate the security crisis... (and engage in) various acts of destruction have been arrested", without giving details about the number of detainees or the timing of the arrests.

The fresh unrest in Africa's second-most populous country comes just nine months after the end of a devastating two-year war in the neighbouring region of Tigray which also drew in fighters from Amhara.

The government said Friday that the emergency measures would cover Amhara "for six months". Still, it could be imposed "nationwide in relation to any situation or movement that aggravates the security problem".

Tensions have been rising since April when the federal government announced it was dismantling regional forces across Ethiopia, triggering protests by Amhara nationalists who said the move would weaken their region.

Clashes in Amhara have escalated in recent weeks, prompting travel warnings from foreign governments and the grounding of flights, with Prime Minister Abiy Ahmed's office on Friday saying emergency measures were needed "to control this unacceptable movement".

According to the emergency decree, anyone found violating its provisions could face "imprisonment of between three to ten years".

The decree also allows for suspects to be searched and held without a warrant.

Under militia control

Local fighters from Amhara's Fano militia have taken control of three towns in the region, residents told AFP.

According to residents of Lalibela, a UNESCO World Heritage site famous for its 12th and 13th-century rock-cut churches, Fano fighters took over the town and its airport earlier this week.

Shops were open on Saturday but streets were largely deserted, Lalibela resident Aneley told AFP.

"Lalibela is calm, no fighting... (but) people's movement isn't like it used to be before," he said, adding that the town was suffering from intermittent power and internet outages.

The mood was similarly tense in the cities of Gondar and Dessie, locals told AFP.

"Things look calm but there is no activity... almost all shops, cafes are closed," said Simachew, a rickshaw driver in Gondar, which witnessed fighting on Thursday before federal troops retreated to its outskirts.

"People are indoors in their homes," he said, with Fano fighters blocking routes in and out of the city.

'On alert'

Amir, a businessman from Dessie, told AFP that there was "no fighting here", with Fano members in control of the city.

"Markets and shops are open but people here are... on alert."

An Amhara resident who fled to the capital Addis Ababa on Saturday said government security forces had "severely restricted" the movement of people in his town of Kobo.

The town "has been under a curfew for a while, with locals prohibited from moving around after dark," he told AFP on condition of anonymity, adding that access to the internet and running water was blocked.

"Fighting has eased for now, but there is a high degree of tension and uncertainty," he said.

The Ethiopian Human Rights Commission on Friday said civilians had been attacked, with damage reported to property, while transport services and the internet had been suspended in some areas of Amhara.

Web security firm Cloudflare told AFP they "saw (internet) traffic in Amhara drop around 18:00 UTC (GMT) on Wednesday".

National carrier Ethiopian Airlines has cancelled flights to Dessie, Lalibela and Gondar.