Six people who inhaled leaking chemicals at the Novartis plant which makes the company's top-selling drug Diovan were taken to hospital on Tuesday, police said.

Novartis had no word on whether production had been affected after the leak of corrosive liquid at the pharmaceutical production site in Schweizerhalle near Basel.

The leak is the latest in a string of problems to hit Novartis manufacturing sites this year.

The drugmaker was cited by U.S. regulators last December for violating manufacturing regulations at three generic drug plants in the U.S. and Canada.

It also suspended production at its consumer health site in Lincoln, Nebraska, to improve quality after consumers complained of chipped and broken pills and inconsistent packaging.

In October, Italy and other European countries temporarily banned the sale of anti-influenza vaccines produced by Novartis after small particles were found in some of the injections, although authorities later lifted the ban.

Police said the leak on Tuesday morning affected 13 people, six of whom were taken to hospital.

They said there was no danger to people outside the site, about 6 km from Basel.

Five of those taken to hospital work for an external cleaning company, while one person was a Novartis employee, police said.

Police said the affected building had been ventilated and returned to its normal state. Investigations are continuing into the cause of the incident.

The Schweizerhalle site manufactures drugs including those used to treat hypertension like blockbuster Diovan, which had sales of $5.7 billion in 2011.

In November 1986, a fire in a storage building used for pesticides and other agricultural chemicals at the Schweizerhalle site released agrochemicals into the air and polluted the Rhine river, turning it red.

At the time, the site belonged to Sandoz, which merged with Ciba-Geigy to form Novartis 10 years later.