From Longman Dictionary of Contemporary Englishseal something ↔ off phrasal verbSTOP something THAT IS HAPPENINGto stop people from entering an area or building, because it is dangerous Following a bomb warning, police have sealed off the whole area. → seal→ See Verb table
Examples from the Corpus
seal off• In Dresden police removed about 3,000 people from the station and sealed it off.• These glades get fainter, and shadows rise to seal them off.• There the whales deliberately tilt the floes so that seals slide off into the water and into the jaws of their attackers.• Press down the edges to seal and trim off the excess pastry. 