15:34 (GMT+4) - The Associated Press news agency is reporting that a helicopter is flying above the Radisson Blu hotel in Mali's capital, Bamako, and that ambulances are "rushing to the hotel".
AP adds that the UN mission in Mali is sending "security reinforcements".
15:25 (GMT+4) - The Reuters news agency is quoting a Turkish government official saying that three Turkish Airlines staff have escaped from the Radisson Blu hotel in Bamako.
Reuters says it's not clear how the three did get out.
There are still four of the airline's staff still thought to be inside the hotel, which gunmen attacked on Friday morning.
14:56 (GMT+4) - At least three hostages were killed as gunmen stormed a luxury hotel in Mali's capital, Bamako, according to reports coming in from AFP news agency.
They quote Mali's security ministry.
14:43 (GMT+4) - Six Turkish Airlines staff members are among those in a luxury hotel attacked by gunmen in Mali's capital Bamako on Friday, a Turkish government official said.
"There are six Turkish Airlines personnel in the hotel," the official told Reuters.
14:26 (GMT+4) - AFP news agency also reports that Mali security forces have escorted two women from the hotel.
14:02 (GMT+4) - The security source said as many as 10 gunmen had stormed the building, firing shots and shouting "Allahu Akbar", or "God is great" in Arabic.
The Chinese state news agency Xinhua said several Chinese tourists were among those trapped inside the building.
The company that runs the hotel, Rezidor Group, said it understood that there were two gunmen.
"According to our information, two people are holding 140 clients and 30 employees," it said in a statement quoted by the BBC.
A senior member of the hotel's security detail said two private security guards had been injured in the early stages of the attack, which began at 7 a.m. (0700 GMT).
Witnesses in the area said police had surrounded the hotel and were blocking roads leading into the neighbourhood.
The U.S. Embassy tweeted that it was "aware of an ongoing active shooter operation at the Radisson Hotel," and instructed its citizens to stay indoors.
An Islamist group claimed responsibility for the death of five people last March in an attack on a restaurant in Bamako that is popular with foreigners.
12:58 (GMT+4) - Gunmen shouting Islamic slogans attacked a luxury hotel full of foreigners in Mali's capital Bamako early on Friday morning, taking 170 people hostage, a senior security source and the hotel's operator said, Reuters reported.
The raid on the Radisson Blu hotel, which lies just west of the city centre near government ministries and diplomatic offices in the former French colony, comes a week after Islamic State (IS) militants killed 129 people in Paris.
The identity of the Bamako gunmen, or the group to which they belong, is not known.
Northern Mali was occupied by Islamist fighters, some with links to al Qaeda, for most of 2012. Although they were driven out by a French-led military operation, sporadic violence has continued.