Merchant seaman Darren McCullagh is in the north African nation on holiday with his girlfriend after serving for several months aboard a merchant vessel.

It's understood that as many as 38 people have been killed in the terrorist violence in Sousse, a town popular with British tourists.

Islamic State extremists have claimed responsibility for the massacre that took place on Friday when holidaymakers were relaxing at the Mediterranean resort.

In an interview with Sky News Darren's mother Moya said her son and his girlfriend witnessed horrific scenes at the beach where the terrorists struck.

She said the couple had taken refuge in a hotel laundry room as the chaos unfolded.

A member of his family later told our reporter the 23-year-old was "safe and well at this moment in time".

Meanwhile, British tourists have started arriving back in the UK with many cheering with relief upon arrival at Gatwick Airport.

It's understood at least five people killed are British nationals, according to the Foreign Office, although in a press conference Tunisia prime minister Habib Essid said the majority of the victims are British.

One gunman suspected of carrying out the deadly attack is thought to have been killed while another is still at large.

One of the many images circulating in the media claims to show a suspect being arrested although it's not clear what role he played in the violence.

A Scottish Government spokeswoman said: "We are closely monitoring the horrifying situation in Tunisia and our thoughts are with those affected and families worried about loved ones.

"The Scottish Government is in contact with the Foreign and Commonwealth Office and we stand ready to offer assistance."

Prime Minister David Cameron said he is "sickened" by the attacks and other recent atrocities in France and Kuwait.

He took to Twitter to say: "Our countries stand together in combating the horrors of terrorism."

The Foreign Office tweeted: "Aware of reports of incident in Tunisia and urgently looking into them. We stand ready to provide consular assistance to British Nationals."

The Foreign Office said people in the UK concerned about relatives in Tunisia should call them on 0207 208 1500.

A spokesman said any British nationals in Tunisia should make contact with the embassy there.