A terrorist arsenal has been discovered during overnight searches in a suburb of Brussels.

Chemicals and explosives were among the items found in the Molenbeek suburb, a rundown neighborhood where Paris attacker Abdelhamid Abaaoud was suspected of operating a terrorist cell.

The find came as Belgium's capital entered a security lockdown. The government has warned that there could be a repeat of Paris-style attacks in the country's capital, prompting the closure of subways in Brussels and the deployment of heavily armed police and soldiers.

At least one Paris attacker, Salah Abdeslam, crossed into Belgium the morning after the Nov. 13 attacks, which killed 130 people last week. A Paris police official and the Paris prosecutor’s office said Saturday they had no firm information on Abdeslam’s whereabouts, including whether he was in the Brussels area.

Prime Minister Charles Michel said the decision to raise the threat level was taken "based on quite precise information about the risk of an attack like the one that happened in Paris ... where several individuals with arms and explosives launch actions, perhaps even in several places at the same time."

Belgium's national Crisis Center raised its terrorism alert for the Brussels region to Level 4, which indicates a "serious and immediate threat." Belgium's special security Cabinet held an emergency meeting Saturday morning.

Heavily armed police and soldiers patrolled Saturday morning at key intersections of the Belgian capital, a city of more than 1 million that is home to the headquarters of the European Union, the NATO alliance and offices of many multinational corporations.

Locals were told to avoid gatherings, train stations, airports and commercial districts. Service was halted on the Brussels Metro, as well as on streetcar lines that run underground.