A worker operating the crane 210ft up in the air has had a heart attack as he climbs down.
The rescue team, from Southsea fire station, will have to get the worker down quickly if he is to stand any chance of survival.
However, on this occasion the daring rescue is luckily just an exercise and the person they are 'saving' is in fact just a dummy.
The 14 firefighters who took part in Wednesday morning's exercise used special high rise rescue equipment for the demonstration as they tested their skills against one of the tallest cranes in the south of England.
The team also got the chance to take in some stunning views of the city from their lofty perch in Goldsmith Avenue, Southsea.
Mark Jones, a crew manager at Southsea fire station, said: 'All our procedures worked well so it was a good exercise all round.
'It is very rare we get the opportunity to practise at such heights so to be given that chance was a great experience.'
The firefighters were invited to perform the exercise by Linden Homes, which operates the crane in the new development next to Pompey's Fratton Park stadium.
After the rescue team reached the dummy, just feet from the top of the crane, firefighter Dave Bird-Newell used a harness to bring it down to a safety point, about halfway down.
From there the team were able to secure the dummy and perform a second descent, taking it down to the ground floor.
The operation actually took about two hours in total, as the firefighters had to respond to emergency calls during the exercise.
Crew manager Jones added: 'The weather was actually okay, there was about a four-foot sway but I think the firefighters were glad we didn't have any big gusts.'