A man armed with a semi-automatic weapon stormed a New Zealand mosque on Friday afternoon local time, in one of two attacks on houses of worship in the city of Christchurch, local police said.

Police arrested four people including the gunman who opened fire at the Masjid Al Noor mosque in the center of the city, killing multiple people there at about 1:40 p.m.

Another shooting occurred at another mosque on nearby Linwood Avenue, authorities said in a press briefing after the shootings.

“This is and will be one of New Zealand’s darkest days,” Prime Minister Jacinda Ardern said after the shootings.

Ardern said that at least 40 people had been killed in the attacks and more than 25 were seriously injured.

Several improvised explosive devices were found in vehicles connected to the suspects — three men and one woman, officials said.

A witness described a scene of carnage after he walked into the Masjid Al Noor mosque to try to help those injured.

“I saw dead people everywhere,” said Len Peneha, who has lived next door to the mosque for about five years.

Peneha said he heard a barrage of shots coming from the mosque after he saw a man dressed in all black walk into the building at about 1:45 p.m. local time.

The gunman then walked out and dropped the semi-automatic weapon in his driveway.

“There were three [dead people] in the hallway, at the door leading into the mosque, and people inside the mosque,” he said. “It’s unbelievable nutty. I don’t understand how anyone could do this to these people, to anyone. It’s ridiculous.”

Local police said in a statement after the shooting, “Police are responding with its full capability to manage the situation, but the risk environment remains extremely high.”

About 300 people were inside for afternoon prayers when the gunman opened fire.

Schools in the city were placed on lockdown after reports of the shooting, the New Zealand Herald reported. Police were unsure if other buildings were under threat.

Another witness to the Masjid Al Noor mosque shooting told the newspaper that she ducked for cover in her car after hearing shots and seeing four or five men running past her.

“When the noise got louder, I saw four or five men running. I put my seat down and lay down so they wouldn’t see me.

“I didn’t think I’d live to see this happening in my country,” she told the newspaper.

The Christchurch City Council also locked down all its buildings after reports of the shooting spread.

“If you were planning on coming into the city center to visit our facilities this afternoon, we urge you to stay away,” the council general manager told a local radio station.

With wires