BOSTON — People taking whale watch cruises out of Boston usually have to travel many kilometres out to sea to spot whales.

But several humpback whales have been spotted in the harbour in the last few days, providing thrills just a half kilometre from downtown Boston.

The Massachusetts Department of Conservation and Recreation posted a video on Twitter of a whale breaching, calling it a “beautiful and rare sight to see.”

A juvenile humpback whale was seen breaching off of Spectacle Island earlier today ???? a beautiful and rare sight to see, captured by @MassDCR while doing routine Boston Harbor Island rounds #conservation #wildlife pic.twitter.com/iqp1Bdak50

— MassDCR (@MassDCR) August 28, 2018

The presence of whales in the busy harbour also comes with a warning. The Coast Guard is urging mariners to use “extreme caution” and keep a safe distance from whales.

A spokeswoman for Boston Harbor Cruises, which offers whale-watching cruises, said company naturalists have identified five to six individual whales.

Experts say they will stick around as long as there is food.