With this year's Run Norwich 10k postponed, athletes have been advised against pounding the pavements on Sunday.
The annual race - which attracted more than 6,000 runners in its last instalment in 2019 - has not taken place for the last two years due to Covid-19.
Organisers announced their decision to delay the event until October 23 on Tuesday lunchtime due to the amber weather warning in the East of England.
Since then some runners have said they'll take on the 10k challenge through the centre of Norwich anyway - though they've been asked not to by the organisers of the event.
Dan Wynne, head of marketing and communication for Norwich City Community Sports Foundation - which runs the event - actively discouraged those looking to do the unofficial 10k.
He said: "I would discourage anyone planning to run the route.
"It is un-stewarded and the roads have not been closed for the race.
"We would ask people to be sensible and consider the heat.
"There won't be medical provision. I would strongly advise people not to take part in any unofficial races on Sunday morning."
Annette Spokes-Ellis is travelling down from her home in Lancashire to Norwich this weekend despite the race being cancelled - but will not be taking on the unofficial 10k.
She ran the "fantastic race" in 2016, 2017 and 2019.
The 47-year-old accounts administrator, who moved away from Norfolk four years ago, said: "We were just coming down for the run really.
"We're not going to waste our trip. We've got everything booked. We could've just given up but we wanted to come down.
"It was a difficult decision for them to make and in the interest of everyone taking part.
"There were casualties being treated at the side of the road when I ran in 2016 and 2017 so it's better to be safe than sorry.
"It's a fantastic race and I thoroughly enjoy it. I'm looking forward to having another weekend in Norwich in October - hopefully the weather will be dry."
Someone not making the trip to Norwich this weekend - or for the rescheduled date - is 32-year-old financial analyst and University of East Anglia graduate Michael Whitmore from Crawley.
He said: "I ran the 2019 race. It's a bit of a bummer really. Everything was hinged on this year's race.
"Originally I was okay with the postponement but the weather's cooled off a bit and I think they've been a bit hasty with it - especially with it being cancelled for the two years before.
"When you book a race in July, you've got to expect warm weather.
"Norwich is a wonderful city. When you have all the volunteers there it makes it feel like a real occasion."
Seasoned runner Alison Armstrong will be running this weekend but has moved her trip out of the city.
She explained: "This weekend we'll go to the coast and do a long run out of Norwich and take in the sea breeze.
Julie Gowland, partner at Birketts Solicitors was due to run the race this weekend with colleagues for charity.
The 41-year-old from Reepham, who is also a member of Reepham Runners, said: "Postponing was not a decision I envy them in making.
"It's such a big event that for many people who perhaps aren't seasoned runners it could very much take its toll.
"The safety of people has to be paramount."
Scott Bemment, 47, is travelling up from London and is planning on doing Brundall parkrun on Saturday morning before doing a solo run of the Run Norwich course on Sunday.
The seasoned runner - who has taken part in every Run Norwich event - said: "I'm just going to do a leisurely run/walk, nothing serious because it is going to be warm.
"I just want to get around the course.
"It's one of the many races in my calendar for this year."
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