Two children have been killed and 20 tourists injured in a head-on crash between two speedboats in Thailand.

The boats were taking holidaymakers on day trips when the smashed into each other off the east coast of Phuket island at 8 am local time. There were 39 people including passengers and crew on the two boats.

CCTV shows the deadly collision. A 12-year-old boy and six-year-old girl, both from Russia, were killed. Paramedics tried to perform CPR on the shore but they were later pronounced dead.

Major Ekachai Siri of the Phuket Tourist Police said the captains of each boat had been detained and questioned.

One of the boats was carrying 39 tourists, understood to be mostly Russian, while four Thai crewmen between the two vessels were uninjured.

Of the 20 injured, at least 10 are said to be in a critical condition. Fifteen people were given immediate medical attention before being discharged.

The incident occurred in the channel linking Phuket's two main marinas with the bay at exactly 8 am local time on Monday (February 10).

Police said that pilots of the two speedboats were being questioned on suspicion of reckless driving causing deaths and injuries. Their paperwork and the licenses to captain the boats were also being checked.

Polic Colonel Prasert Srikhunrat said that the 'Payan 5' vessel, operated by Seastar company, was travelling from Laem Nga in Rassada to pick tourists up at Royal Phuket Marina when the accident happened.

While the Payan 5 was turning into the access channel to arrive at Royal Phuket Marina, it was struck by another boat, the “ALP” operated by LP company.

The police chief said: ''At this time, the investigation into the collision is still ongoing. Officers will inspect the scene of the accident before travelling to see the injured persons at the hospitals next.''