Experts say better staffing numbers will be key to improving bowel-cancer screening.

The screening age is set to lower to 58 for Northland, Auckland and the South Island today, with the rest of the North Island to follow in March.

More than 120,000 people will qualify for screening in the first year of this change, and the Government aims to boost colonoscopy capacity to lower the age screening age further.

But colorectal surgeon Frank Frizelle says there's plenty of capacity to expand it, but more resources are needed.

"The Government is walking very cautiously in this line, because it's worried that its resources won't be able to deliver. To me, it doesn't seem to match up."

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