At least four Thai nationals have been killed and about 36 others were injured, including 10 foreigners, according to Anurak Amornpetchsathaporn with the Ministry of Public Health.
No one has claimed responsibility for the blasts, and it's not clear if the bombings are connected.
Thai police say there's no evidence the attacks are related to international terrorism.
"These incidents are different from the usual terrorism acts. They are more local sabotage on certain locations and provinces," Deputy Police Spokesman Maj. Gen. Piyapan Pingmuang said at a news conference Friday.
Political unrest has in recent years roiled Thailand
, resulting at times in protests. The series of blasts comes days before the first anniversary of the Erawan Shrine bombing
, which killed 20 people, and five days after the country voted on a new constitution
Pingmuang said the explosions are not linked to the Erawan bombing.
Following his weekly address to the nation, Thai Prime Minister Prayut Chan-o-cha denounced the blasts, telling the country -- and the world -- that the perpetrators will be brought to justice.
"I express my condolences to those deaths and injuries -- both Thais and foreigners," he said. "My government will take care and provide full support and we will investigate on this and bring those behind these attacks to legal prosecution with our best ability."
The prime minister also called on the public to remain vigilant and exercise caution while visiting tourist hotspots, reminding locals to report anything unusual to officials immediately.
"All Thais must help each other unitedly to achieve stability and safety," Chan-o-cha added, referring to the recent political turmoil following the constitutional referendum. "We won't create any conflicts with anyone., we must not blame each other. Thais must be united as one."
The first explosion occurred at 3 p.m. local time in Trang province, killing one man and injuring six people, according to the Royal Thai Police.
Two bombs went off that evening in the resort city of Hua Hin -- one at 10:15 p.m. near a bar called Johnny's 56, and another at 11 p.m. in front of the Rain Tree Spa.
A woman working at a food vending cart was killed, Police Lieutenant Colonel Samoer Yoosumran said.
Royal Thai Police said another 21 people were wounded.
They include citizens from Italy, Germany, the Netherlands and Austria, according to Thomas Mohr with the San Paulo Hospital in Hua Hin.
Shane Brett, who was visiting the area from Tokyo, said he was close by during both explosions.
He told CNN that he heard a "bang" and saw people panicking around the area.
"[I] went to have a look and caught a glimpse of the scene but the whole area was in frenzy and people [were] advised to stay inside," he said.
Security at the Hilton hotel where Brett is staying has dramatically increased, he said.
Police Lieutenant Colonel Samoer Yoosumran said the bombs had been placed in tree planters near the targets.
Edwin Wiek, who has lived in Thailand for almost 30 years, tweeted a photo of a planter that was blown apart in one of the blasts.
Multiple attacks Friday
On Friday morning at least eight explosions occurred in five provinces.
Bombs went off again Hua Hin as well as in Surat Thani, Trang Province, Phang-nga province and the resort island of Phuket.
Two bombings in Phuket happened at 7:45 a.m. and 8:45 a.m. on Friday, according to Royal Thai Police.
The explosions hit Patong Beach and Bang La Street -- both popular tourist sites -- said Major General Theerapol Thipcharoen, the chief of Phuket Provincial Police.
One person suffered minor injuries in the Phuket incident, authorities said.
In Surat Thani city, two explosions occurred at 8:01 a.m. and 8:30 a.m. local time. The blasts occurred about 650 feet apart from each other, local Police Captain Chavalit Chanmornoi told CNN.
The 8:01 a.m. blast killed a female municipal worker.
Chanmornoi said four people were injured in the incident, though the Police put the number of wounded at three.
Two bombs also went off in the Bang Miang market in Phang-nga province at 9 a.m., the Police said. No one was injured.
Back in Hua Hin, another two bombs placed in tree planters went off at 9 a.m. and 9:05 a.m. near a clock tower, a city landmark, according to Royal Police.
"Police have tightened security," Yoosumran said. "We have set up check points and inspecting bags and other things."
Many of the Friday blasts occurred near seaside resorts -- but in the early morning, before crowds would have gathered to soak up the sun.
However, the bombs were not particularly big and most beach resorts were on high alert after a bomb was found in Phuket Wednesday night, Paul Quaglia, a Thailand security expert and 20-year veteran of the CIA, told CNN.
Quaglia also said the bombings are likely not related to the recent constitutional referendum, as it would be difficult to plan and execute coordinated explosions in such a short time.
Friday is Mother's Day in Thailand, which is a public holiday.
Hua Hin is a popular coastal resort, about 90 miles southwest of the Thai capital, Bangkok. The city is home to many international hotel chains, including the Marriott, Hilton and Hyatt.
It's also home to the Klai Kangwon Palace, the seaside residence of Thailand's King Bhumibol Adulyadej.
The palace is located less than a mile from the site of the bombing.
The island of Phuket is one of Thailand's most popular destination for foreign tourists. Patong beach is lined with cafes and bars, while the district's Bang La Road is known as one of Thailand's more raucous nightlife hotspots.
By Friday afternoon, things seemed to be getting back to normal in Phuket -- bars were beginning to open and the police presence was gone, Hong Kong-based freelance journalist Andrew Scott told CNN.
"People really don't seem to care," Scott, who lived in Phuket for five years, told CNN over the phone. "Just as long as they can do what they want to do with their holiday."