Dozens of people were still unaccounted for following a deadly Islamist attack on Mozambique's northern town of Palma, while thousands of survivors were being evacuated to the provincial capital Pemba, various sources said. 

Militants began attacking the town, a gas hub in the province of Cabo Delgado, on Wednesday, forcing nearly 200 workers, including foreign employees, to evacuate a hotel where they had taken refuge.

They were temporarily taken to the heavily guarded gas plant located on the Afungi peninsula on the Indian Ocean coast south of the Tanzanian border before being moved to Pemba.

The Department of Foreign Affairs said: "The very small number of Irish nationals known to have been in the area of Cabo Delgado are confirmed safe.

"Embassy Maputo is monitoring the situation closely and is in contact with the Mozambique authorities as well as the UN and other international agencies on the ground."

Some residents of the town of around 75,000 people fled to the peninsula - home of a multi-billion-dollar gas project being built by France's Total and other energy companies.

A boat that left Afungi yesterday landed in Pemba around midday, according to police patrolling the city port. 

According to a source close to the rescue operation, there were "about 1,400" people on board. 

The evacuees included non-essential staff of Total and Palma residents who had sought refuge at the gas plant.

Several other small boats packed with displaced people were on their way to Pemba and expected to arrive overnight or tomorrow morning, according to humanitarian aid agencies.

Airport officials in Pemba said humanitarian aid flights had been suspended to free up space for military operations.

Caritas, a Catholic aid agency which is active in the province, also reported new arrivals to Pemba, located around 250km south of Palma.

Human Rights Watch said the militants indiscriminately shot civilians in their homes and on the streets.

"A rescue operation is currently under way. An unknown number of people died as they tried to flee Amarula hotel," Human Rights Watch regional director Dewa Mavhinga told AFP, adding their rescue convoy "was attacked by the insurgents".

The militant attack on Palma is the closest yet to the major gas project during a three-year Islamist insurgency across Mozambique's north.

Since October 2017, extremist fighters have raided villages and towns in the region, forcing nearly 700,000 to flee their homes.

The violence has left at least 2,600 people dead, half of them civilians, according to the US-based data-collecting agency Armed Conflict Location and Event Data (ACLED).

A South African worker was killed in the Palma violence, according to a government source in his native country.

While local media reports said British workers may also have been caught in the attack, the UK's Foreign Commonwealth and Development Office said its embassy in Maputo was in "direct contact with authorities in Cabo Delgado to urgently seek further information on these reports".

"The UK wholeheartedly condemns the appalling violence in Cabo Delgado. It must stop," Minister for Africa, James Duddridge, tweeted.

The US, whose troops are helping train Mozambican troops fight the insurgency, said it "continues to monitor the horrific situation in Palma", adding one American citizen who was in Palma had been safely evacuated.

The embassy announced earlier this month that American military personnel will spend two months training soldiers in Mozambique.