The insecticide can damage people's kidneys, liver and thyroid glands if eaten in large quantities. However, food standards agencies are playing down the risks for anyone who has already eaten the tainted eggs.
Which countries are affected?
Farms were shut down in the Netherlands, Belgium, Germany and France after authorities confirmed that fipronil had been used, European Commission spokesman Daniel Rosario said on Friday.
The EU countries that have received the eggs are the UK, Sweden, Austria, Ireland, Italy, Luxembourg, Poland, Romania, Slovenia, Slovakia and Denmark. Non-EU Switzerland is also affected.
Friday's revelation that tainted eggs had also been sent to Hong Kong marks the first time the widening scandal has spread outside Europe.
The Food Standards Agency (FSA) said it was very unlikely that there was a risk to public health.
Processed foods containing eggs, including sandwiches and salads, have been recalled by leading supermarkets, including Sainsbury's, Morrisons, Waitrose and Asda.
Supermarkets in Belgium, the Netherlands and Germany have also withdrawn millions of eggs from sale.
On Friday, France's Agriculture Minister Stéphane Travert said about 250,000 affected eggs had been sold in the country since April, adding that all products containing eggs from contaminated farms would be taken off the shelves.
In Hong Kong, the government's Centre for Food Safety says it identified two samples of imported Dutch eggs containing excessive levels of fipronil last week and asked shops to remove the products.
It has since tested other European egg imports and has not found any more "unsatisfactory samples", the South China Morning Post newspaper quoted a spokeswoman as saying.
What will the EU meeting do?
"Blaming and shaming will bring us nowhere and I want to stop this," European Commissioner for Health and Food Safety Vytenis Andriukaitis said on Friday.
"But first things first. Our common job and our priority now is to manage the situation, gather information, focus on the analysis and lessons to be learned in a view to improve our system and prevent criminal activity."
A commission spokesperson later added that the event scheduled for 26 September was not a crisis meeting. It is unclear whether the meeting will involve all 28 EU member states, or only affected countries.
What's happening with the criminal investigation?
On Thursday, Dutch police arrested two people in joint raids carried out with Belgian authorities.
A criminal investigation is under way, centring on two firms. Poultry Vision, a pest control firm from Belgium, is alleged to have sold the treatment to a Dutch poultry farm cleaning company, Chickfriend.
More than 100 poultry farms have been closed during the investigation, and 26 suspects identified and evidence seized from their companies.
Why have countries been arguing?
The Netherlands is Europe's biggest egg producer - and one of the largest exporters of eggs and egg products in the world.
The problem first surfaced earlier in August, when supermarket chain Aldi withdrew all its eggs from sale in Germany.
It has since emerged that Belgian officials knew about the contamination in June, but did not make the information public.
Meanwhile, Belgian Agriculture Minister Denis Ducarme has accused the Dutch authorities of knowing about the problem as far back as November 2016. The food watchdog in the Netherlands has denied this.
I'm in the UK - should I stop eating eggs?
By James Gallagher, health and science reporter, BBC News
Fipronil should not be allowed anywhere near food.
But the risk from eggs is thought to be low, because the number of contaminated eggs is also low.
While 700,000 eggs sounds like a lot, it is worth remembering we eat 34 million every single day in the UK.
It is why the Food Standards Agency says it is "very unlikely" there is any health risk.
Many of the affected eggs will have already passed through the food chain before anyone was aware of the scandal.
And the FSA has now pulled egg sandwiches and egg salads off the shelves that were made while contaminated eggs were still being imported.
It insisted there is "no need" for people to stop eating eggs.