At least 31 people have been killed during a stampede at a charity event in southern Nigeria’s Port Harcourt city on Saturday (May 28), according to the Associated Press.

A witness named Daniel said “there were so many children” among the dead. Five of the dead children were siblings, he told the Associated Press. He added that a pregnant woman was also among those that lost their life.

The event was organized by the Kings Assembly Pentecostal church in Rivers state and it involved hundreds of people who had showed up to receive free food and other goods at the church’s annual “Shop for Free” charity event, according to Grace Iringe-Koko, a police spokeswoman.

Iringe-Koko stated that the donation drive was supposed to start at 9 a.m. but dozens of people arrived as early as 5 a.m. to secure their spot in line. The crowd apparently forced their way into the church, despite the fact that the gate was locked, causing the stampede.

“People were there earlier and some got impatient and started rushing, which led to stampeding. The police are on the ground monitoring the situation while the investigation is ongoing,” Iringe-Koko told Reuters.

Seven others were injured but are “responding to treatment,” said Iringe-Koko. The event was suspended while authorities launched an investigation on how the stampede occurred.

According to another witness Christopher Eze, some of the church members were attacked and injured by relatives of the victims after the stampede. The church has declined to comment on the situation.

Nigeria has seen similar stampedes in the past. In 2013, twenty-four people died at an overcrowded church gathering in the southeastern state of Anambra. In 2014, at least 16 people were killed when a crowd got out of control during a screening for government jobs in the country’s capital, Abuja.