'The enemy is ever ready to pounce,' says Mugabe

President Robert Mugabe has told Zimbabweans to remain vigilant on the country's 37th anniversary of independence - as his main rival Morgan Tsvangirai bemoaned the "stinking poverty" so many here live in.

Frequently losing his place as he read out a lacklustre speech to crowds gathered at the National Sports Stadium, the 93-year-old president said: "We celebrate as a vigilant nation."

"The enemy is ever ready to pounce on any sign of laxity and weakness on our part," he added.

Zimbabwe's economic problems are worsening, with high unemployment, little foreign investment and shortages of cash.

In a likely sign of the president's fear of falling, Mugabe was driven straight to the podium to deliver his speech.

He always used to walk into the stadium. But an embarrassing stumble on the red carpet in 2015 focused attention on his walk in public, which these days is extremely slow.

Crowds cheered and whistled continuously during his speech. But it wasn't clear how attentively they were listening to the president.

The one moment a round of applause did break out was when the Zimbabwe leader - who's been in power since independence in 1980 - made an unusual appeal for tolerance of those from different political parties.

"People have a right to belong to the party of their choice... So let them pursue their own chosen lives as they desire," Mugabe said.

Elections are due in Zimbabwe in 2018.

Polls since 2000 have been marred by intimidation, allegations of rigging and in some cases violence directed against supporters of the opposition Movement for Democratic Change.

MDC-T leader Morgan Tsvangirai said in a message to mark independence day: "Every Zimbabwean must ask themselves whether we really deserve this suffering in a country for which so many paid the ultimate sacrifice."