US President Donald Trump has accused Barack Obama of tapping his phone during the US election.

In a series of early morning tweets, the president alleged his predecessor had his wires tapped in Trump Tower last October.

President Trump compared the situation to Watergate.

He also described the alleged phone tap as "McCarthyism", referring to the political witch hunt that marred US politics in the 1950s. 

He also says a good lawyer could "make a great case" out of the allegation.

However, he did not indicate the source of the information.