\documentclass{standalone}

\usepackage{tikz}

\usetikzlibrary{positioning}

% To convert the document to a png:

% magick convert -density 200 -trim filename.pdf -quality 100 filename.png

\begin{document}

\begin{tikzpicture}[

latentnode/.style={circle, draw=red!80, minimum size=6mm, very thick},

observednode/.style={circle, draw=red!80, fill=cyan!60, minimum size=6mm, very thick},

]

% Defining the nodes

\node[latentnode, label=above right:{${\bf z}_1$}] (z1) {};

\node[latentnode, label=above right:{${\bf z}_2$}] (z2) [right=of z1] {};

\node (transition) [right=of z2] {$\ldots$};

\node[latentnode, label=above right:{${\bf z}_{N-1}$}] (z_nm1) [right=of transition] {};

\node[latentnode, label=above right:{${\bf z}_{N}$}] (zn) [right=of z_nm1] {};

\node[latentnode, label=above right:{${\bf z}_{N+1}$}] (z_np1) [right=of zn] {};

\node (final) [right=of z_np1] {};

% Defining observed nodes

\node[observednode, label=above right:{${\bf x}_1$}] (x1) [below=of z1]{};

\node[observednode, label=above right:{${\bf x}_2$}] (x2) [below=of z2]{};

\node[observednode, label=above right:{${\bf x}_{N-1}$}] (x_nm1) [below=of z_nm1]{};

\node[observednode, label=above right:{${\bf x}_{N}$}] (xn) [below=of zn]{};

\node[observednode, label=above right:{${\bf x}_{N+1}$}] (x_np1) [below=of z_np1]{};

% Relationships between latent variables

\draw[->, color=red, very thick] (z1) -- (z2);

\draw[->, color=red, very thick] (z2) -- (transition);

\draw[->, color=red, very thick] (transition) -- (z_nm1);

\draw[->, color=red, very thick] (z_nm1) -- (zn);

\draw[->, color=red, very thick] (zn) -- (z_np1);

% final node

\draw[->, color=red, very thick] (z_np1) -- (final);

% Relationships between observed and latent variables

\draw[->, color=red, very thick] (z1) -- (x1);

\draw[->, color=red, very thick] (z2) -- (x2);

\draw[->, color=red, very thick] (z_nm1) -- (x_nm1);

\draw[->, color=red, very thick] (zn) -- (xn);

\draw[->, color=red, very thick] (z_np1) -- (x_np1);

\end{tikzpicture}

\end{document}