Stifling regulations are preventing China's 1.4 billion people from accessing several common vaccines available in much of the rest of the world, raising public health risks and posing a challenge to global pharmaceutical companies in a huge potential market.

Sam Ding, a tech professional in southern China, says he crossed the border to Hong Kong twice to get his one-year-old daughter a key vaccine for potentially fatal conditions -- pneumonia, blood infections and meningitis.

Why Hong Kong? The pneumococcal vaccine from Pfizer that he was looking for wasn't available on the mainland.

At the heart of Ding's troubles is a massive pharmaceutical market where demand is outstripping the ability of regulators to keep up, forcing patients to scramble for many essential vaccines and hindering the ability of multinationals to bring them in. The Chinese vaccine market is estimated to grow at around 17 percent a year to hit 40 billion yuan ($6 billion) in 2018 from about 25 billion yuan last year, McKinsey & Co. estimates based on research reports. But more than 30 vaccine products identified by top multinationals as major revenue generators in other parts of the world aren't sold on the mainland, according to the consultancy.

"For multinationals there are hurdles to bring key products to market, including registration timelines," said Franck Le Deu, senior partner at McKinsey.

Public faith in China's vaccine system suffered another blow recently after police in Shandong province in eastern China arrested a mother-daughter team for allegedly selling more than 570 million yuan ($88 million) worth of vaccines illegally in 18 provinces since 2011. Local police said the pair distributed products that may have been improperly stored and transported, the official Xinhua news agency reported, without specifying whether the brands they sold were local or foreign.

While the improperly stored vaccines could possibly be ineffective, they were very unlikely to be toxic, the WHO said. But the scandal still stirred waves of outrage on social media and on online public forums.

Ding said he was willing to travel to Hong Kong twice because he felt it was very important that his daughter get the pneumococcal vaccine. "After she was born I was more worried about pneumonia," he said. "China's environmental hygiene isn't very good and it's so densely populated, pneumonia is a serious matter."

The pneumococcal vaccine has gradually disappeared from mainland China after Pfizer's license to sell the shot expired a year ago. Chinese regulators are yet to approve Pfizer's latest version of the vaccine, called Prevenar 13, which sells all over the world.

China has no other approved pneumococcal vaccines for children under two, although the shot is among those recommended by the World Health Organization for all countries. The Asian country requires companies to conduct local clinical trials on Chinese for products already approved elsewhere, sometimes with higher criteria for approvals than required by the WHO, leading to many years of delay before they become available.

Vaccines made by Merck and Glaxo for HPV, or the human papillomavirus that can cause cervical cancer, are recommended by the World Health Organization for all countries. They are also not available in China and both companies have pending applications to sell them. The China Food and Drug Administration didn't respond to a fax seeking comment.

Ding says he had to pay an agency a 50 percent mark-up to arrange the first shot for his daughter in Hong Kong. After the faulty vaccines were found in China, Hong Kong said only 120 children who weren't Hong Kong residents would be allowed to get vaccinated at public hospitals per month. Mainland Chinese flock to Hong Kong for everything from baby food to cancer medicines, and the city a few years ago put restrictions on the number of formula tins that could be taken across the border to curtail shortages.

Pfizer in an email said it is continuing to work with Chinese authorities for registration and approval of its pneumococcal vaccine. "Prevenar 13 is included in the pediatric National Immunization Programs of 102 countries and is approved in more than 150 countries across the world," the company said.

Merck submitted clinical trial data for its HPV vaccine Gardasil to the China Food and Drug Administration in 2012 and its application remains under review by the regulatory agency, according to an e-mailed statement from the company. Glaxo declined to comment on products that are currently in the regulatory process.

First proved 10 years ago, Gardasil is now licensed in 130 countries, and recently reported by the U.S. Centers for Disease Control and Prevention to reduce prevalence of the types of HPV it covers in teenage girls by 64 percent, Merck said. China is estimated to have close to 100,000 new cervical-cancer cases last year, according to a recent study based on the National Central Cancer Registry of China published in a journal.

"The vaccines that WHO recommends for all countries are important to the health of children; otherwise, WHO would not recommend the vaccines for all countries," the international agency said via email.

The world's largest pharmaceutical companies are already facing a roadblock in China as a state-led campaign to slash drug prices has triggered a slowdown in sales growth. Lengthy approval processes add to those difficulties.

"It means missed opportunities for multinationals and patients," said McKinsey's Le Deu.