Fighting and gunfire erupted in South Sudan's capital on Monday a day after the UN Security Council told rivals President Salva Kiir and Vice-President Riek Machar to rein in their forces and end days of violence.

Scores of people have been killed in the fighting which first erupted on Thursday between Kiir loyalists and supporters of Machar, who led rebels during a two-year civil war. Renewed clashes have raised fears of a return to full-blown conflict.

South Sudan's capital was rocked Sunday by heavy arms fire between forces loyal to the president and those of the vice-president, causing widespread casualties and raising fears the country is returning to civil war.

The fighting in Juba began in the morning and continued until about 8 p.m. local time Sunday, when a large thunderstorm seemed to put a damper on the violence, said United Nations mission spokeswoman Shantal Persaud. She confirmed that a UN armoured personnel carrier was hit by a shell at a camp to protect civilians. UN peacekeepers in the vehicle were wounded, said witnesses.

"The condition is really very bad. We have a lot of casualties this side, I think around 50 to 60 besides those of yesterday," said Budbud Chol who oversees security at a clinic in the base. "We have civilian casualties. We have rocket-propelled grenades that have landed in the camp which has wounded eight people." Among the wounded are five children and two women while the rest were men, he said.

At least one person has died in the camp, he said, but he did not know about casualties outside where the fighting was heavy.

The opposition side blamed government forces for starting the fighting Sunday morning with an attack on a rebel base in the Jebel area of the capital. Three helicopter gunships bombed rebel camps, said William Gatjiath Deng, a spokesman for the rebel forces.

South Sudan's army confirmed the Sunday clashes but it is not clear how the fighting started, said army spokesman Lul Ruai Koang, who is in the SPLA general headquarters at Bilpham.

Canada closes embassy

The Canadian government has closed its embassy in Juba "until further notice" and warned Canadians in the country to consider leaving as soon as it's safe to do so.

"Be aware that the ability of Canadian officials to provide consular assistance in South Sudan is extremely limited. The situation in Juba is deteriorating," reads a Global Affairs advisory sent to Canadian nationals in South Sudan.

"Many security checkpoints have been set up throughout the country, making road travel difficult. Remain indoors, away from windows and doors, and monitor the security situation closely. The airport may be closed on short notice and travel to the airport may be difficult if not impossible."

Canada has also issued an online advisory warning Canadians to avoid all travel to the country.

UN holds emergency meeting

The UN Security Council was holding a closed emergency meeting Sunday afternoon for consultations on the fighting in South Sudan. UN Secretary General Ban Ki-moon condemned the fighting.

"I am shocked and appalled by the heavy fighting that is currently taking place in Juba. I strongly urge President Kiir and First Vice-President Riek Machar to do everything within their power to de-escalate the hostilities immediately and to order their respective forces to disengage and withdraw to their bases," said Ban in a statement. "This senseless violence is unacceptable and has the potential of reversing the progress made so far in the peace process."

Ban confirmed that UN compounds and sites to protect civilians in Juba have been caught in the crossfire.

"We called this meeting because the situation is spiraling out of control. We are extremely worried by what appears to be the lack of command and control over the troops," said Samantha Power, the U.S. Ambassador to the UN, adding that the attacks on civilians and UN sites are "deplorable."

10,000 flee

About 10,000 Juba residents fled neighbourhoods where there was fighting, said Jeremiah Young, policy advisor for World Vision in South Sudan.

"We have seen quite a few individuals packing up and leaving, trying to find shelter, what look like a lot of civilians taking off down the street, carrying their suitcases, their children," he said.

Other residents said they could not leave because of the fighting.

"I've gotten calls that I should leave but there was so much gunfire nearby I decided to stay in," said one resident, who insisted on anonymity for her safety.

The fighting on Sunday appeared to be mainly in two areas: Jebel, where there is an opposition base and a UN base which houses thousands of internally displaced people, and in Gudele, where the rebels have another opposition base, including Machar's compound. There were huge explosions in Gudele and people are fleeing by foot, said a resident, who spoke on condition of anonymity for fear for her safety.

"The situation in Juba has significantly deteriorated," said a statement by the United States embassy. "There is serious fighting between government and opposition forces, including near the airport, UN mission locations, Jebel and elsewhere throughout Juba. U.S. citizens in Juba should remain vigilant ... shelter in a safe location, preferably away from doors and windows, and avoid non-essential movements."

Precarious calm shattered

Sunday's fighting was a resumption of the conflict on Friday in which more than 100 people died. A precarious calm was restored on Saturday— the day South Sudan marked its fifth independence day — that was shattered Sunday by the fighting.

South Sudan is trying to emerge from a two-year civil war caused by political rivalry between Vice-President Machar and President Kiir.

A similar clash in December 2013 sparked of the civil war that killed tens of thousands of people.​