Nine passengers have jumped from a hot air balloon hovering over Melbourne's Port Phillip Bay onto a police boat below following fears the balloon, which was low on fuel, would ditch into the water.

The balloon was hovering about 500 metres offshore around Black Rock and low on fuel, the Metropolitan Fire Brigade (MFB) said.

Fireboat crews and water police travelled to the scene about 8:30am, while a number of nearby fishing boats trailed the balloon.

The balloon floated over the police boat and each time it began to lose altitude, passengers climbed out of the basket and jumped onto the deck below.

The passengers were taken to the Beaumaris motor yacht squadron to be checked by paramedics.

The loss of passengers reduced the weight of the basket, allowing the pilot to return to shore. The balloon then landed at Mount Martha.

'Occasionally we land in strange spots'

Pilot Peter Wright, who has been flying for 20 years, said he had earlier tried to land in a park in Brighton.

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"As I approached the park, my flight path was taking me towards a tall light pole, so I obviously had to go over the light pole but with the speed that I had I was unable to get the balloon into the park ... safely," he said.

"I saw on my map I had a parkland near the beach ... and when I got there it was all full of trees. That was when I realised I needed a bit of luck to go my way."

He said he then climbed back up to try and use the wind to get the balloon back, but given its speed and direction, decided to contact authorities as a precaution to help land safely.

Mr Wright said the whole situation went "smoothly" and the passengers were "fabulous, very cooperative and calm".

He said they never ran out of fuel, but given he had been in the air for about two hours, supplies were running low.

"Ballooning is one of those things. Occasionally we do land in strange spots. Apart from taking up the time of the fabulous water police, it's all been OK," he said.

"I followed our procedures, they worked perfectly."