At least 9 people were wounded in a bomb blast in the Thai capital Bangkok on Sunday, local media reported.

A bomb, hidden in a black plastic bag, went off at a bus station in front of Big C supermarket in Bangkok's Water Gate area, a main shopping and tourism center, all injured were rushed to hospital, one of them in serious condition.

Two cars were also damaged from the explosion, the Bangkok Post online said. Police were investigating the incident and believed the explosive was a homemade bomb inside a garbage bag at the bus stop.

The police have suspended traffic near the Ratchaprasong intersection to allow forensic officials to collect evidence.

No group has claimed responsibility for the bombing so far.

Sunday's blast happened when the ruling Democrat Party candidate Panich Vikitsreth is set to win a parliament by-election in Bangkok.

Panich won 52.77 percent of the votes, while 40.93 percent voted for opposition Puea Thai Party candidate Korkaew Pikulthong, according to an exit poll.

The Election Commission is expected to announce the unofficial result around 08:00 p.m. Sunday.

Pitting a leader of the red-shirts movement, detained on terrorism charges, against a member of the ruling Democrat Party, the election was seen as a public opinion after the red-shirts' anti-government protest was put to an end by force on May 19 in central Bangkok.

The violent protest lasted over two months and left more than 80 dead and about 2,000 injured.