A man in Paris attacked police officers with a hammer on Tuesday near Notre Dame Cathedral, and he was shot and wounded by police.
One officer has minor injuries, the BBC reports, while the assailant has been hospitalized.
Authorities are investigating the incident as a terrorist attack, NPR's Eleanor Beardsley reports.
"Paris is on alert after terrorist attacks in London over the weekend killed seven people," Eleanor says. "Paris police say the situation is under control."
Immediately afterward, Notre Dame — one of Paris' most popular tourist destinations — was put on lockdown, with about 900 people inside, Eleanor reports.
"French TV showed footage of many people sitting on the stone floor," she said Tuesday. "They are being told to remain calm and stay put until police wrap up their security operation."
A few hours later, the people trapped inside the church began being released one by one, The Associated Press reports.
The attacker was armed with kitchen knives and a hammer, Interior Minister Gerard Collomb told reporters, according to the AP. The man had documents "suggesting he was an Algerian student," the wire service reported, citing the interior minister.
Collomb said the man shouted, "This is for Syria."
Former U.S. Ambassador to the U.N. Nancy Soderberg was among the hundreds of people trapped inside the cathedral after the attack, the AP reports.
Soderberg told the news service that "everyone was very quiet and very scared" as police examined each of the cathedral's pews, but that everything inside the cathedral was calm and orderly.