Key Points:

A total of 65 people at an international badminton tournament in Christchurch have fallen foul of a mystery vomiting and diarrhoea bug.

Just five more people have become ill since yesterday, leading Canterbury medical officer of health Alistair Humphrey to believe the illness may have nearly run its course.

While the cause and identity of the sickness have yet to be established, suspicions are on a shared meal on Good Friday for the 170 trans-Tasman under 17-tournament participants.

"It seems at this point to be the only thing in common with everybody, that's when everybody got together," Dr Humphrey told NZPA.

"It may or may not be the food at the dinner; it could simply be because somebody was infected with something like a norovirus and it was spread at the dinner."

He said some of the latest five to fall ill had already been feeling a bit off-colour yesterday, so they might not be part of a "second wave" of the sickness.

"I think we'll see it blow over today actually."

Many of those sick were already making good recoveries and nobody's health was at serious risk.

Testing was underway to identify the sickness.

Nobody from outside the tournament had reported similar symptoms.

Play was cancelled at the tournament as participants sought medical treatment.

Dr Humphrey said affected people had moved into accommodation with others similarly affected in a bid to stop any spread.

Tournament director Lyndsay Dick, who also suffered from the illness, described the outbreak as "pretty unfortunate".