Brussels' terror alert status will remain at the maximum level, while the city's schools and metros are to stay shut on Monday.
Belgian police say a number of operations are underway across the country in response to terror threats referred to by Prime Minister Charles Michel.
He has confirmed the situation is extremely serious.
In Brussels, a bus can be seen blocking a road in the city centre and armed police are guarding the area.
However federal police are asking local residents and the media not to disclose the exact location of the armed forces.
Threat of ‘coordinated, multiple attacks’
Speaking prior to the operations, the prime minister announced the capital’s terror alert status would remain at the highest level, citing a threat of “coordinated, multiple attacks.”
The rest of Belgium will remain on a threat level of three, on a four-tier scale.
Michel said the city’s metro network would remain closed and schools in Brussels would also be shut on Monday (November 23).
The prime minister also said that he would seek to reduce events attracting large crowds.
“The threat is considered to be the same as yesterday: serious and imminent. We’re continuing to focus particular attention on the public transport system and I confirm that the decision has been made to keep the metro closed on Monday,” Michel announced.
Eyewitnesses say local residents have been asked to stay indoors and away from their windows.
One eyewitness described the scene in Brussels city centre to Belgian news site RTL:
“I was at a restaurant and the police asked us to finish our meals and to group together inside. They said to wait for their signal before leaving.”
Certain branches of the BNP Paribas bank will be asking employees to work from home, while others will be asking for clients to prove their identity before allowing access.
#Belgium: Maximum alert in #Brussels - risk of attack with weapons and explosives @CharlesMichelpic.twitter.com/XAHGmhDIRP— euronews (@euronews) November 21, 2015
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