A drone captured footage of a mother whale giving birth in front of a tour boat off Dana Point, California (Picture: AP)

Tourists in California were treated to a once-in-a-lifetime experience when they witnessed a mother whale give birth to a calf up close.

Pacific gray whales are a common sight for whale watchers sailing with Captain Dave’s Dolphin & Whale Safari in Dana Point, California. They estimate they see about 1,000 per year during their migratory period – which typically lasts from December to May.

But nobody onboard was expecting to see the spectacle they witnessed on Monday: a 35-foot long mother gray whale give birth and show off her calf to three boats full of people.

‘This is a first for all of us,’ the captain says over the loudspeaker. ‘We’ve never seen this actually happen.’

‘We’ve seen babies shortly after they were born, we’ve seen baby dolphins that were less than an hour old,’ Captain Dave’s co-president Gisele Anderson told Metro.co.uk. ‘But this is a first.’

The footage was captured by cameras and cell phones on each of the company’s three boats, as well as overhead footage captured by a drone.

When crew members on board Captain Dave’s vessels first spotted the whale, they were worried she was injured or entangled due to the amount of blood in the water.

‘It went from horror to pure joy and astonishment,’ Boat Captain Gary Brighouse told the Orange County Register.

Crew members were originally worried that the mother whale was injured. Captain Dave’s sends special teams out to rescue injured and entangled whales throughout the year (Picture: AP)

In the video, the mother whale can be seen pushing her newborn to the surface. ‘The mother’s first order of business is to get the baby to the surface,’ Anderson said. ‘It’s incredible that they are born knowing not to breathe underwater.’

The mother then directs her calf to swim up close to one of the smaller boats.

Typically, Pacific gray whales give birth after a one year gestation period in shallow lagoons in Baja California – most notably in San Ignacio Lagoon, Magdalena Bay, and Laguna Ojo de Liebre.

After giving birth, the mother whale directs her baby to the surface to breathe (Picture: AP)

Gray whales make a 5,000 mile trek from their feeding grounds in the northern Pacific Ocean to reach their preferred breeding spots. ‘This baby came about 600 miles too soon,’ Anderson said.

Anderson said she has witnessed gray whales direct their calves to interact with people in the Baja California lagoons, teaching them not to fear humans. She called the entire experience on Monday ‘humbling.’

‘Just 70 years ago – well within the lifetime of some of these whales – human beings were still hunting whales,’ she said. ‘This mother is trusting us – a former predator – with her baby.’

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‘This is a first for all of us,’ the captain says over the loudspeaker. ‘We’ve never seen this actually happen.’