A high school in Colorado, one of the first two US states to legalise recreational marijuana use, was put on partial lock down after a student's weed pipe filled a classroom with pot smoke, the school said.

The smoke from the device, known as a "gravity bong" or "bucket", was released into a classroom at Adams City High School in Commerce City, a northeastern suburb of Denver.

"As a precautionary measure, our students were placed on a modified lock down to limit movement throughout the school," the school said in a statement, adding that teenagers who had been near the device were examined by medical personnel.

"As always, students' safety is our number one priority," it said. "All students were fine and the school is resuming business as usual."

The school said it was working with the proper authorities to resolve the issue, and that it would provide more information when available. It did not give details on the student who brought the pipe to class, nor possible disciplinary measures.

Colorado voted in 2012 to allow recreational marijuana sales to adults aged 21 and older beginning this year. But consumption of the drug by minors, or by anyone in public settings such as schools, parks and on the street, remains illegal.

The tale of the partial lock down received widespread attention on social media, with some Denverites describing it as the story of the day and an "only in Colorado" moment.

A gravity bong or bucket uses the force of gravity, normally by releasing water from a chamber, to suck a large amount of pot smoke into a container, from where it is inhaled by the user.