At least 29 people in Liberia including 11 children and a pregnant woman, have died in a stampede of worshippers at a Christian ceremony in a densely populated area of the capital, Monrovia, officials said on Thursday.

The stampede erupted when a gang of thugs armed with knives attacked some of the hundreds attending the ceremony at about 9pm on Wednesday, police spokesman Moses Carter told the Associated Press.

One person has been arrested, he said.

The Rev Abraham Kromah, who was holding the ceremony and who runs a church in the New Georgia township of Monrovia, was also brought in for questioning about the incident, police said.

The bodies have been taken to the morgue of Redemption Hospital, close to where the incident occurred in a beach area called New Kru Town.

Street gangs have become an increasing problem in Monrovia and other Liberian cities in recent years, according to residents.

Liberian president, George Weah, visited the scene on Thursday and declared three days of national mourning.

“Moving forward,” he said there should be regulations on how these ceremonies, which Liberians call crusades, are conducted. The measures, he said, should limit the number of people who can attend based on the size of the crusade grounds.

Even though “we all are religious people,” everyone should be willing to comply with these regulations for safety reasons, he added.