Armed police have sealed off a property in Wakefield Road, Dewsbury.
There was also police presence in Old Bank Road this afternoon after a Black BMW was involved in a crash at around 2.30pm.
It is understood an unmarked police vehicle rammed into the car.
Eyewitnesses report an arrest being made.
Police are refusing to confirm any more details for “operational reasons”, sparking frenzied speculation on social media.
Some people claimed to have heard gunshots near Manor Croft Academy, but on Facebook Lorna Tagg said: “There was no gun shots at Manor Croft Academy as my daughter goes to that school and I am sure she would have known if there was.”
A spokesman for the National Crime Agency said they were not involved in the operation.
Click here for the latest on this story.