Pol Col Kong-ath Suwankham, the Mayor district police chief, said a hospital employee phoned the police after he saw a suspicious man parking a motorbike with a side car outside the hospital. The man, who wore a helmet and a black shirt, then rushed to another motorbike and fled.
According to the witness, he heard a loud explosion just under 10 minutes after he made the phone call.
The blast wounded a 25-year-old woman and her son. The two were on a motorbike passing through the area. A hospital staff member, aged 29, was also injured in the attack. The three were now safe.
A bomb disposal team found a damaged motorbike and pieces of a gas tank scattered around the area.
Pol Col Kong-ath said police were able to identify at least five suspects involved in the motorcycle bombing. So far, four of them had been arrested and taken to a military regiment for further questioning.