Officials at the UN say between 100 and 150 people from its 9,000-strong peacekeeping mission in Haiti are still missing after the earthquake.
UN Secretary-General Ban Ki-moon listed 16 peacekeeping soldiers and police who are known to have died.
The UN said it urgently needed medical support and rescue teams with heavy lifting equipment.
The head of UN peacekeeping, Alain Le Roy, said UN police and troops in Haiti had secured the port and airport.
They were also patrolling and helping clear roads, he added.
Top officials missing
Among those missing are UN mission head Hedi Annabi of Tunisia and his chief deputy, Luis Carlos da Costa.
Hedi Annabi is a Tunisian diplomat
Edmond Mulet, Mr Annabi's predecessor, is on his way to Port-au-Prince to take charge of the peacekeeping mission in an interim capacity.
Ten Brazilian peacekeepers, three from Jordan and a Haitian staff member are among those confirmed to have died.
China's state media said eight Chinese were dead and 10 more missing.
The UN said earlier that at least 56 of its staff had been injured in the earthquake.
The Minustah mission has been in Haiti since 2004, following the ousting of President Jean-Bertrand Aristide.
Its mandate is to maintain law and order in the impoverished and often violent state and to administer security during election periods.
Minustah, an acronym from the French Mission Nations Unies de Stabilisation en Haiti, has about 9,000 multinational peacekeepers. Brazil is the biggest contributor and is in charge.
Brazilian anxiety
A UN logistical base near the airport is functioning and the UN expects to get an emergency response team on the ground shortly.
Brazil took charge of the Minustah operation in 2004.
The BBC's Gary Duffy in Sao Paulo says that given Brazil's central role the earthquake has caused a lot of concern and shock.
He says it has been a desperately worrying time for the families of the more than 1,200 Brazilian soldiers in the UN mission.
Some soldiers have managed to make contact to reassure relatives, but given the damage to infrastructure at Brazilian bases, communication is proving difficult, even for the government, our correspondent says.
Brazil's leadership of the UN mission has been difficult, amid continuing gang violence.
Minustah has been criticised by business leaders for being too lenient and by rights groups for using excessive force.