Rwandan-backed M23 rebels have entered Bukavu, the second-largest city in the eastern Democratic Republic of Congo, seizing the regional governor's office.

Some people lined the streets to clap and cheer the fighters as they marched and drove into the city centre without resistance. It is the second city after Goma to fall to the rebels in the mineral-rich region in the past few weeks.

The Congolese government has acknowledged its fall and urged residents to stay at home "to avoid being targeted by the occupying forces".

The UN and European countries have warned that the latest offensive, which has seen hundreds of thousands of people forced from their homes, could spark a wider regional war.

A resident in Bukavu, who asked to remain anonymous because of concerns for her safety, told the BBC on Sunday that most people were still afraid to leave their homes.

"Since yesterday the children and the youth took the weapons. They are shooting everywhere in all directions, they are looting," she said.

"This morning the M23 entered and they were acclaimed by the people, very happy to see them. We don't know if it's because they are afraid or because they found that there were no authorities in the city.

"The place where I live the crackling [gunfire] can still be heard."

On Friday, the M23 captured Bukavu's main airport, which is about 30km (18 miles) north of the city - and then began advancing slowly towards the city, which is the capital of South-Kivu province.

The provincial governor, Jean-Jacques Purusi Sadiki, confirmed to the Reuters news agency the fighters were in Bukavu city centre by Sunday morning, adding that Congolese troops had withdrawn to avoid urban fighting.

This left a security vacuum in the city on Saturday with chaotic scenes playing out, including a reported prison break from the central prison.

The UN World Food Programme (WFP) said a warehouse with nearly 7,000 tonnes of food was looted.

The city of around two million people on the southern tip of Lake Kivu borders Rwanda and is an important transit point for the local mineral trade.

Its fall represents an unprecedented expansion of territory for the M23 since their latest insurgency started in late 2021 - and is a blow to the government of President Félix Tshisekedi.

Government spokesman Patrick Muyaya said Rwanda was violating DR Congo's territorial integrity through expansionist ambitions and human rights abuses.

The Congolese government accuses Rwanda of sowing chaos in the region - as well as having troops on the ground - so it can benefit from its natural resources, something Kigali denies.

President Tshisekedi wants his Rwandan counterpart Paul Kagame to face sanctions over the latest unrest.

But President Kagame has dismissed such threats - and has repeatedly pointed out that Rwanda's main priority is its security.

He has long been angered by what he sees as the failure of the Congolese authorities to deal with the DR Congo-based FLDR rebel group, which he sees as a danger to Rwanda.

The group is made up of some members of the ethnic Hutu militia accused of involvement in the 1994 genocide in Rwanda when over 100 days around 800,000 people, mainly from the Tutsi ethnic group, were killed.

Troops from the Tusti-led M23 gathered at the Place de l'Indépendance in central Bukavu on Sunday, where one of its commanders, Bernard Byamungu, was filmed chatting to locals and answering their questions in Swahili.

He urged government forces "hiding in houses" to surrender - and accused the withdrawing military of spreading terror by arming local youths who had gone on a looting rampage.

The African Union (AU) - which has been holding a heads of state summit in Ethiopia this weekend - again urged the M23 to disarm.

"We are all very, very concerned about an open regional war," Reuters quotes the AU's peace and security commissioner Bankole Adeo as saying.