A resident of the West Point district told the Associate Press by phone that security forces were firing into the air to disperse crowds angry over the quarantine measures. Reuters reported that police fired tear gas at the angry residents.
The New York Times reported that men hurled rocks and a teenager appeared to be injured by a bullet during the melee.
People could be seen gathering at roadblocks just outside the West Point area to complain that they had been cut off from their homes. The restrictions made it difficult to get a full picture of what was happening in the sealed-off neighborhood.
Fear and tension have been building in Monrovia for days and West Point has been one of the flash points. Many residents feel the government has not done enough to protect them from the spread of Ebola.
West Point residents raided an Ebola screening center over the weekend, accusing officials of bringing sick people from all over Monrovia into their neighborhood. In many areas of the capital, meanwhile, dead bodies have lain in the streets for hours, sometimes days, even though residents asked that the corpses be picked up by Health Ministry workers wearing protective gear.
The Ebola outbreak, which began in December, has killed at least 1,229 people in Guinea, Liberia, Sierra Leone and Nigeria.
Liberia has the highest death toll, and its number of cases is rising the fastest. In response, President Ellen Johnson Sirleaf ordered West Point sealed off and imposed a nighttime curfew, saying authorities have not been able to curtail the spread of Ebola in the face of defiance of their recommendations.
Sirleaf also ordered gathering places like movie theaters and night clubs shut and put Dolo Town, 30 miles (50 kilometers) south of the capital, under quarantine as well.
"These measures are meant to save lives," she said in an address Tuesday night.
On Wednesday, riot police and soldiers created roadblocks out of piles of scrap wood and barbed wire to prevent anyone from entering or leaving West Point, which occupies a peninsula where the Mesurado River meets the Atlantic Ocean.
Few roads go into the area, and a major road runs along the base of the isthmus, serving as a barrier between the neighborhood and the rest of Monrovia. Ferries to the area have been halted, and a coast guard boat was patrolling the waters around the peninsula.
At least 50,000 people live on the half-mile-long (kilometer-long) point, which is one of the poorest and most densely populated neighborhoods of the capital. Sanitation is poor even in the best of times, and defecation in the streets and beaches is a major problem.
Mistrust of authorities is rampant in this poorly served area, where many people live without electricity or access to clean water.
A woman who called into a local radio station's breakfast program said she was blocked in traffic because there was a protest in West Point by disgruntled youths opposed to the quarantine. Others protested just outside the quarantine area at a roadblock to complain that they had been cut off from their homes.
One resident said that police were firing into the air to try to break up the crowds. He spoke on condition of anonymity to protect his safety.
While whole counties and districts in Sierra Leone and Liberia have been put under quarantine and internal travel restrictions have limited the movement of people in Guinea, the West Point quarantine was the first time such restrictions have been put in place in a capital city.
The current Ebola outbreak is the most severe in Liberia and Sierra Leone, but the U.N. health agency said that there were encouraging signs that the tide was beginning to turn in Guinea. There is also hope that Nigeria has managed to contain the disease to about a dozen cases
Nigeria's health minister, Onyebuchi Chukwu, said Tuesday that a fifth person had died of the disease in that country. All of Nigeria's reported cases so far have been people who had direct contact with a Liberian-American man who was already infected when he arrived in the country on an airliner.