Feng Lili and his 4-year-old son were hospitalized at Daping Hospital in Chongqing after they drank hot chocolate contaminated with disinfectant at a local McDonald's restaurant on Monday. LI WENBIN/CHINA DAILY

A father and son were hospitalized on Monday after drinking hot chocolate containing disinfectant at a McDonald's in Chongqing.

Feng Lili, 46, took his 4-year-old son into a McDonald's at noon on Monday and ordered a kid's meal, which included a hot chocolate drink.

The son took a sip of the chocolate and refused to drink more. Feng thought maybe the drink was too hot and asked the son to wait until it cooled down. After the son finished the meal, Feng found the drink almost untouched and decided to drink it himself, according to Chongqing Evening News.

"I had a gulp of the drink and it tasted a little bit sour," Feng was quoted as saying. "I thought it might be Sprite. But when I took a second sip, I found something was wrong."

After about 10 seconds, Feng felt burns on his tongue and in his throat.

He took the drink to the counter and told the employees about his symptoms.

The staff admitted that the hot water bottle had been full of disinfectant while the restaurant was doing routine sterilizing, but the staffer thought it was hot water and poured it into Feng's drink.

The McDonald's workers then went with the father and son to Daping Hospital.

According to the Chongqing Liangjiang Food and Drug Administration, the son has recovered and the father is still in the hospital under medical observation.

"The McDonald's staff mistakenly added 250 grams of disinfectant (cyanuric acid) to Feng's hot chocolate," a statement by the administration said. An investigation is underway.

"McDonald's has been dedicated to providing our customers with safe and high-quality food, and we sincerely apologize for the misconduct at our store," said a McDonald's news release sent to China Daily on Tuesday afternoon.

"We will take action to solve the problem with the customer, and strengthen our management and staff training to prevent incidents like this from happening again."

Feng declined to comment on the incident.

Deng Rui contributed to this story.