At least six explosions hit two Thai cities in a span of about 12 hours, police officials told CNN.

Two bombs went off in the resort of Hua Hin Friday morning near the clock tower, a city landmark, according to Police Lieutenant Colonel Samoer "The bombs went off while we were working on site, they were not very far from each other," Yoosumran said. "Police have tightened security. We have set up check points and inspecting bags and other things."

Around 650 feet (200 meters) away, another two bombs exploded late Thursday as foreign tourists were leaving local bars to go back to their hotels, Yoosumran said.

At least 11 people -- mostly foreign visitors -- were injured and a woman who had a food vending cart in front of a bar was killed Thursday night, according to Yoosumran.

"The bombs were planted on the street where most of the customers are foreigners," he told CNN earlier. "And they went off while foreigners started to leave the bars and go back to their hotels."

Second city hit

Further south, at least one person, a female municipal worker, was killed and four injured Friday after two blasts went off in in Surat Thani city, in the southern Thailand's Surat Thani Province, according to Chavalit Chanmornoi, a local police captain.

The explosions occured about about 650 feet (200 meters) from each other, and were around 30 minutes apart, Chanmornoi said.

No one has claimed responsibility for the blasts -- and it's not clear if they're connected.

The series of blasts come days before the one year anniversary of the Erawan Shrine bombing, which killed 20 people.

A popular resort town

Hua Hin is a popular coastal resort, about 90 miles (145 kilometers) 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 (about 2 kilometers) from the bombing site.

Resort town blasts

Both bombs that exploded in Hua Hin Thursday night were planted inside tree pots, about 164 feet (50 meters) away from each other, near a bar called Johnny's 56, Yoosumran said.

The first bomb went off at around 11 p.m. local time. The second exploded a few minutes later, Yoosumran said.

Edwin Wiek, who has lived in Thailand for almost 30 years, said one bomb was near the London Bar, not far from the Hua Hin Beach.

He tweeted a photo of a planter that was blown apart in one of the blasts.

A video he took shows an emergency responder examining items found on the ground next to a food cart.

(CNN)