By Ben Hirschler

BASEL, Switzerland (Reuters) - Drugmakers said on Monday they would continue to ship medicines to Greece in coming weeks, despite mounting unpaid bills, but warned supplies could be in jeopardy if Europe did not take emergency action.

"In the worst-case scenario of ‘Grexit’, we believe the

integrity of the medicines supply chain may be in jeopardy, which would create a risk to public health," the industry's trade association said in a letter to the European Commission.

A copy of the letter to EU Health Commissioner Vytenis Andriukaitis from Richard Bergstrom, director general of the European Federation of Pharmaceutical Industries and Associations, was seen by Reuters.

Imports of life-saving medicines, along with energy, top the list of products at risk if Greece defaults on its debt and moves closer to exiting the euro zone.

Drug manufacturers face moral pressure not to cut off supplies and an emergency meeting of the Hellenic Association of Pharmaceutical Companies agreed on Monday to ensure supplies continued for the coming month.

But despite the action of individual companies there might still be shortages unless special steps are taken to stop the diversion of supplies to other countries.

Bergstrom said global companies like Roche (ROG.VX), Novartis (NOVN.VX), Pfizer (PFE.N) and Sanofi (SASY.PA) wanted to find a way to keep drugs flowing but needed support from the European Commission.

If Greece leaves the euro zone and reintroduces the drachma, the value of the new currency is likely to depreciate rapidly, creating a significant arbitrage opportunity for traders to re-export medicines to other European countries.

Such so-called parallel trade is allowed under European free trade rules but drugmakers argue temporary curbs should be considered by European authorities to prevent drug shortages in Greece.

Drug supplies could also be at risk from a more general breakdown in trading systems, since the Greek medicines supply chain is complex and involves several hundred wholesalers, who purchase and distribute drugs to pharmacies.

Reuters reported last month that drug companies were owed more than 1.1 billion euros ($1.2 billion) by Greek hospitals and the state-run health insurer EOPYY, after not being paid since December.

Greece represents less than 1 percent of world drugs sales but it could have a bigger knock-on effect on the wider market due to parallel trade and the practice of other countries referring to Greek prices for their own price setting.

(Editing by David Holmes)